feat: add v2 character card import/export

- Expanded Character struct with all v2 spec fields (description, scenario, mes_example, post_history_instructions, alternate_greetings, character_book, tags, creator, character_version, creator_notes, extensions)
- Created CharacterCardV2 serialization structs following spec at github.com/malfoyslastname/character-card-spec-v2
- Implemented PNG metadata utilities:
  * read_character_card_from_png() - extracts and decodes character data from PNG tEXt chunks
  * write_character_card_to_png() - embeds character data into PNG files
  * create_placeholder_png() - generates gradient placeholder images for avatarless characters
- Added Tauri commands:
  * import_character_card - opens file picker, imports PNG with automatic name conflict handling
  * export_character_card - exports character as v2 PNG card with embedded metadata
- Added Import/Export buttons to character settings UI
- Full backward compatibility with existing characters using serde defaults
- Added dependencies: png 0.17, base64 0.21, image 0.24

src-tauri/Cargo.lock

@@ -270,6 +270,12 @@ version = "0.22.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "72b3254f16251a8381aa12e40e3c4d2f0199f8c6508fbecb9d91f575e0fbb8c6"
 
+[[package]]
+name = "bit_field"
+version = "0.10.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1e4b40c7323adcfc0a41c4b88143ed58346ff65a288fc144329c5c45e05d70c6"
+
 [[package]]
 name = "bitflags"
 version = "1.3.2"
@@ -501,6 +507,12 @@ dependencies = [
  "windows-link 0.2.1",
 ]
 
+[[package]]
+name = "color_quant"
+version = "1.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3d7b894f5411737b7867f4827955924d7c254fc9f4d91a6aad6b097804b1018b"
+
 [[package]]
 name = "combine"
 version = "4.6.7"
@@ -613,12 +625,37 @@ dependencies = [
  "crossbeam-utils",
 ]
 
+[[package]]
+name = "crossbeam-deque"
+version = "0.8.6"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9dd111b7b7f7d55b72c0a6ae361660ee5853c9af73f70c3c2ef6858b950e2e51"
+dependencies = [
+ "crossbeam-epoch",
+ "crossbeam-utils",
+]
+
+[[package]]
+name = "crossbeam-epoch"
+version = "0.9.18"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5b82ac4a3c2ca9c3460964f020e1402edd5753411d7737aa39c3714ad1b5420e"
+dependencies = [
+ "crossbeam-utils",
+]
+
 [[package]]
 name = "crossbeam-utils"
 version = "0.8.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d0a5c400df2834b80a4c3327b3aad3a4c4cd4de0629063962b03235697506a28"
 
+[[package]]
+name = "crunchy"
+version = "0.2.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "460fbee9c2c2f33933d720630a6a0bac33ba7053db5344fac858d4b8952d77d5"
+
 [[package]]
 name = "crypto-common"
 version = "0.1.6"
@@ -858,6 +895,12 @@ version = "1.0.20"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d0881ea181b1df73ff77ffaaf9c7544ecc11e82fba9b5f27b262a3c73a332555"
 
+[[package]]
+name = "either"
+version = "1.15.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "48c757948c5ede0e46177b7add2e67155f70e33c07fea8284df6576da70b3719"
+
 [[package]]
 name = "embed-resource"
 version = "3.0.6"
@@ -962,6 +1005,21 @@ dependencies = [
  "pin-project-lite",
 ]
 
+[[package]]
+name = "exr"
+version = "1.73.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "f83197f59927b46c04a183a619b7c29df34e63e63c7869320862268c0ef687e0"
+dependencies = [
+ "bit_field",
+ "half",
+ "lebe",
+ "miniz_oxide",
+ "rayon-core",
+ "smallvec",
+ "zune-inflate",
+]
+
 [[package]]
 name = "fastrand"
 version = "2.3.0"
@@ -1324,6 +1382,16 @@ dependencies = [
  "wasi 0.14.7+wasi-0.2.4",
 ]
 
+[[package]]
+name = "gif"
+version = "0.13.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4ae047235e33e2829703574b54fdec96bfbad892062d97fed2f76022287de61b"
+dependencies = [
+ "color_quant",
+ "weezl",
+]
+
 [[package]]
 name = "gimli"
 version = "0.32.3"
@@ -1497,6 +1565,17 @@ dependencies = [
  "tracing",
 ]
 
+[[package]]
+name = "half"
+version = "2.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "6ea2d84b969582b4b1864a92dc5d27cd2b77b622a8d79306834f1be5ba20d84b"
+dependencies = [
+ "cfg-if",
+ "crunchy",
+ "zerocopy",
+]
+
 [[package]]
 name = "hashbrown"
 version = "0.12.3"
@@ -1818,6 +1897,24 @@ dependencies = [
  "icu_properties",
 ]
 
+[[package]]
+name = "image"
+version = "0.24.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5690139d2f55868e080017335e4b94cb7414274c74f1669c84fb5feba2c9f69d"
+dependencies = [
+ "bytemuck",
+ "byteorder",
+ "color_quant",
+ "exr",
+ "gif",
+ "jpeg-decoder",
+ "num-traits",
+ "png",
+ "qoi",
+ "tiff",
+]
+
 [[package]]
 name = "indexmap"
 version = "1.9.3"
@@ -1947,6 +2044,15 @@ version = "0.3.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "8eaf4bc02d17cbdd7ff4c7438cafcdf7fb9a4613313ad11b4f8fefe7d3fa0130"
 
+[[package]]
+name = "jpeg-decoder"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "00810f1d8b74be64b13dbf3db89ac67740615d6c891f0e7b6179326533011a07"
+dependencies = [
+ "rayon",
+]
+
 [[package]]
 name = "js-sys"
 version = "0.3.81"
@@ -2008,6 +2114,12 @@ version = "1.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "bbd2bcb4c963f2ddae06a2efc7e9f3591312473c50c6685e1f298068316e66fe"
 
+[[package]]
+name = "lebe"
+version = "0.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7a79a3332a6609480d7d0c9eab957bca6b455b91bb84e66d19f5ff66294b85b8"
+
 [[package]]
 name = "libappindicator"
 version = "0.9.0"
@@ -3012,6 +3124,15 @@ dependencies = [
  "unicode-ident",
 ]
 
+[[package]]
+name = "qoi"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "7f6d64c71eb498fe9eae14ce4ec935c555749aef511cca85b5568910d6e48001"
+dependencies = [
+ "bytemuck",
+]
+
 [[package]]
 name = "quick-xml"
 version = "0.37.5"
@@ -3161,6 +3282,26 @@ version = "0.6.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "20675572f6f24e9e76ef639bc5552774ed45f1c30e2951e1e99c59888861c539"
 
+[[package]]
+name = "rayon"
+version = "1.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "368f01d005bf8fd9b1206fb6fa653e6c4a81ceb1466406b81792d87c5677a58f"
+dependencies = [
+ "either",
+ "rayon-core",
+]
+
+[[package]]
+name = "rayon-core"
+version = "1.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "22e18b0f0062d30d4230b2e85ff77fdfe4326feb054b9783a3460d8435c8ab91"
+dependencies = [
+ "crossbeam-deque",
+ "crossbeam-utils",
+]
+
 [[package]]
 name = "redox_syscall"
 version = "0.5.18"
@@ -4051,8 +4192,11 @@ dependencies = [
 name = "tauri-app"
 version = "0.1.0"
 dependencies = [
+ "base64 0.21.7",
  "bytes",
  "futures",
+ "image",
+ "png",
  "reqwest",
  "serde",
  "serde_json",
@@ -4370,6 +4514,17 @@ dependencies = [
  "syn 2.0.106",
 ]
 
+[[package]]
+name = "tiff"
+version = "0.9.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ba1310fcea54c6a9a4fd1aad794ecc02c31682f6bfbecdf460bf19533eed1e3e"
+dependencies = [
+ "flate2",
+ "jpeg-decoder",
+ "weezl",
+]
+
 [[package]]
 name = "time"
 version = "0.3.44"
@@ -5128,6 +5283,12 @@ dependencies = [
  "windows-core 0.61.2",
 ]
 
+[[package]]
+name = "weezl"
+version = "0.1.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a751b3277700db47d3e574514de2eced5e54dc8a5436a3bf7a0b248b2cee16f3"
+
 [[package]]
 name = "winapi"
 version = "0.3.9"
@@ -5844,6 +6005,15 @@ dependencies = [
  "syn 2.0.106",
 ]
 
+[[package]]
+name = "zune-inflate"
+version = "0.2.54"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "73ab332fe2f6680068f3582b16a24f90ad7096d5d39b974d1c0aff0125116f02"
+dependencies = [
+ "simd-adler32",
+]
+
 [[package]]
 name = "zvariant"
 version = "5.7.0"