feat: add character avatars with upload and zoom functionality

- Add avatar upload with file picker dialog
- Display avatars in header, chat messages, and settings
- Implement clickable avatars with full-screen zoom modal
- Enable asset protocol for local file access in Tauri config
- Add tauri-plugin-dialog for native file selection
- Store avatars in ~/.config/claudia/avatars/
- Support PNG, JPG, JPEG, and WEBP formats
- Modal closes on overlay click or ESC key

src-tauri/Cargo.toml

@@ -18,8 +18,9 @@ crate-type = ["staticlib", "cdylib", "rlib"]
 tauri-build = { version = "2", features = [] }
 
 [dependencies]
-tauri = { version = "2", features = [] }
+tauri = { version = "2", features = ["protocol-asset"] }
 tauri-plugin-opener = "2"
+tauri-plugin-dialog = "2"
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 reqwest = { version = "0.12", features = ["json", "stream"] }