feat(ai): disable local provider and improve commit file display

Local AI is now treated as unavailable in the settings UI, with a
migration to ensure any previously saved "local" selection switches
back to OpenAI. The history panel also improves how commit file
names are presented, including clearer old->new path formatting.

- Migrate stored AI provider away from local to prevent dead state
- Disable local provider option with an "in development" badge
- Refine history panel filename rendering and tooltip context

src/lib/components/AiSettingsDialog.svelte

@@ -141,9 +141,16 @@
 
     <form class="ai-settings-form" onsubmit={(e) => { e.preventDefault(); void handleSave(); }}>
       <div class="ai-provider-options" role="radiogroup" aria-label="AI provider">
-        <button type="button" class="ai-provider-option" class:active={provider === "local"} onclick={() => { provider = "local"; }}>
+        <button
+          type="button"
+          class="ai-provider-option ai-provider-option-local"
+          class:active={provider === "local"}
+          disabled
+          title="Local AI is still in development and not yet available"
+        >
           <Cpu size={16} aria-hidden="true" />
           Local AI
+          <span class="ai-provider-badge">In development</span>
         </button>
         <button type="button" class="ai-provider-option" class:active={provider === "openai"} onclick={() => { provider = "openai"; }}>
           <Bot size={16} aria-hidden="true" />