feat: make context limit configurable in API settings

Add context limit field to API settings that:
- Stores context limit in config (defaults to 200000)
- Allows users to set custom limits for different models
- Uses configured limit in token counter display
- Shows format like "2.5k / 200k tokens" using actual limit

This allows proper token tracking for non-Claude models with
different context windows.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

src/index.html

@@ -350,6 +350,19 @@
               </select>
             </div>
 
+            <div class="form-group">
+              <label for="context-limit">Context Limit (tokens)</label>
+              <input
+                type="number"
+                id="context-limit"
+                placeholder="200000"
+                value="200000"
+                min="1000"
+                step="1000"
+              />
+              <small style="color: var(--text-secondary); margin-top: 4px; display: block;">Maximum tokens for model context (e.g., 200000 for Claude)</small>
+            </div>
+
             <div class="form-group">
               <label>
                 <input type="checkbox" id="stream-toggle" />

src/main.js

@@ -1457,6 +1457,7 @@ async function handleSaveSettings(e) {
   const apiKey = document.getElementById('api-key').value.trim();
   const model = document.getElementById('model-select').value;
   const stream = document.getElementById('stream-toggle').checked;
+  const contextLimit = parseInt(document.getElementById('context-limit').value) || 200000;
   const saveBtn = document.getElementById('save-settings-btn');
   const validationMsg = document.getElementById('validation-message');
 
@@ -1472,7 +1473,7 @@ async function handleSaveSettings(e) {
   setStatus('Saving configuration...', 'default');
 
   try {
-    await invoke('save_api_config', { baseUrl, apiKey, model, stream });
+    await invoke('save_api_config', { baseUrl, apiKey, model, stream, contextLimit });
     validationMsg.textContent = 'Configuration saved successfully';
     validationMsg.className = 'validation-message success';
     setStatus('Configuration saved', 'success');
@@ -1661,10 +1662,18 @@ async function updateTokenCount() {
         currentInput
       });
 
+      // Get context limit from config
+      let contextLimit = 200000; // Default
+      try {
+        const config = await invoke('get_api_config');
+        contextLimit = config.context_limit || 200000;
+      } catch (e) {
+        // Use default if config not available
+      }
+
       // Update total display
       const tokenCounter = document.getElementById('token-counter');
       const tokenCountTotal = document.getElementById('token-count-total');
-      const contextLimit = 200000; // Claude 200k context
 
       // Format: "2.5k / 200k tokens"
       tokenCountTotal.textContent = `${formatTokenCount(tokenData.total)} / ${formatTokenCount(contextLimit)} tokens`;
@@ -3339,6 +3348,7 @@ async function loadExistingConfig() {
     document.getElementById('api-base-url').value = config.base_url;
     document.getElementById('api-key').value = config.api_key;
     document.getElementById('stream-toggle').checked = config.stream || false;
+    document.getElementById('context-limit').value = config.context_limit || 200000;
 
     const modelSelect = document.getElementById('model-select');
     modelSelect.innerHTML = ''; // Clear existing options