feat: apply Charbon·Lime design system, add gear icon, multi-provider git settings

- Replace app icon with new Charbon·Lime brand assets (icon.png + adaptive-icon.png)
- Apply design tokens to theme.ts: bg #1B2433, primary/success #88D656 (lime), text1 #EEF2F5 (cream)
- Add ⚙ gear button (lime) in HomeScreen header → navigates to /settings
- Expand settings: git provider selector (Gitea / GitHub / GitLab) with per-provider fields
- Add lib/git.ts: unified pushIncidentToGit() for Gitea, GitHub (PUT), and GitLab APIs
- Update incident detail screen to use lib/git.ts and dynamic provider routing

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

app.json

@@ -5,12 +5,13 @@
     "version": "0.1.0",
     "orientation": "portrait",
     "userInterfaceStyle": "dark",
-    "backgroundColor": "#0f1117",
+    "icon": "./assets/icon.png",
+    "backgroundColor": "#1B2433",
     "scheme": "sheethappens",
     "android": {
       "adaptiveIcon": {
         "foregroundImage": "./assets/adaptive-icon.png",
-        "backgroundColor": "#0f1117"
+        "backgroundColor": "#1B2433"
       },
       "package": "fr.gyozamancave.sheethappens",
       "permissions": [