feat: deliver P2 v0.2.0 with unified editor, search, and snapshots

Implement schema v2 migration, outline/setting/inspiration CRUD, unified TipTap editing, reference panel with mentions, FTS global search, chapter version history, writing landmarks, word frequency analysis, light theme contrast fixes, and full unit/E2E test coverage.

Co-authored-by: Cursor <cursoragent@cursor.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "bilin",
-  "version": "0.1.0",
+  "version": "0.2.0",
   "description": "笔临 - 长篇创作智能协作平台",
   "main": "./out/main/index.js",
   "type": "module",
@@ -28,6 +28,7 @@
     "@tiptap/extension-underline": "^3.27.1",
     "@tiptap/react": "^3.27.1",
     "@tiptap/starter-kit": "^3.27.1",
+    "diff-match-patch": "^1.0.5",
     "electron": "^36.9.0",
     "i18next": "^24.2.3",
     "jotai": "^2.12.1",
@@ -39,6 +40,7 @@
   },
   "devDependencies": {
     "@playwright/test": "^1.51.0",
+    "@types/diff-match-patch": "^1.0.36",
     "@types/node": "^22.13.0",
     "@types/react": "^18.3.18",
     "@types/react-dom": "^18.3.5",