feat(git-diff): add Lezer-based syntax highlighting

- Add @lezer/highlight and language parsers (JS/TS, JSON, CSS, HTML, Python, Markdown)
- Create syntax-highlighter utility that parses code with Lezer and returns highlight tokens
- Integrate highlighting into diff view with color-coded tokens
- Keywords (purple), strings (green), numbers (orange), functions (blue), types (yellow), etc.
- Highlighting respects add/remove line backgrounds

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

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/app/package.json

@@ -18,6 +18,14 @@
     "@boudra/expo-two-way-audio": "^0.1.3",
     "@expo/vector-icons": "^15.0.2",
     "@gorhom/bottom-sheet": "^5.2.6",
+    "@lezer/common": "^1.5.0",
+    "@lezer/css": "^1.3.0",
+    "@lezer/highlight": "^1.2.3",
+    "@lezer/html": "^1.3.13",
+    "@lezer/javascript": "^1.5.4",
+    "@lezer/json": "^1.0.3",
+    "@lezer/markdown": "^1.6.2",
+    "@lezer/python": "^1.1.18",
     "@react-native-async-storage/async-storage": "2.2.0",
     "@react-navigation/bottom-tabs": "^7.4.0",
     "@react-navigation/elements": "^2.6.3",