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/app.css

@@ -1721,6 +1721,19 @@
     color: #f5f7ff;
     background: linear-gradient(180deg, rgba(100,108,255,0.22), rgba(65,209,255,0.1));
   }
+  .ai-provider-option-local {
+    flex-wrap: wrap;
+    row-gap: 2px;
+  }
+  .ai-provider-badge {
+    flex-basis: 100%;
+    text-align: center;
+    font-size: 9.5px;
+    font-weight: 700;
+    letter-spacing: 0.04em;
+    text-transform: uppercase;
+    color: var(--color-ink-faint);
+  }
   .ai-local-profile-options {
     display: grid;
     grid-template-columns: repeat(3, minmax(0, 1fr));