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>

tests/main/snapshot.repo.test.ts

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+import { describe, it, expect, beforeEach, afterEach } from 'vitest'
+import { DatabaseSync } from 'node:sqlite'
+import { migrate } from '../../src/main/db/migrate'
+import { SnapshotRepository } from '../../src/main/db/repositories/snapshot.repo'
+import { VolumeRepository } from '../../src/main/db/repositories/volume.repo'
+import { ChapterRepository } from '../../src/main/db/repositories/chapter.repo'
+import type { SqliteDb } from '../../src/main/db/types'
+
+describe('SnapshotRepository', () => {
+  let db: SqliteDb
+  let repo: SnapshotRepository
+  let chapterId: string
+
+  beforeEach(() => {
+    db = new DatabaseSync(':memory:')
+    migrate(db)
+    repo = new SnapshotRepository(db)
+    const vol = new VolumeRepository(db).create('卷一', 0)
+    chapterId = new ChapterRepository(db).create(vol.id, '第一章', 0, '初始内容').id
+  })
+
+  afterEach(() => {
+    db.close()
+  })
+
+  it('creates and lists snapshots', () => {
+    repo.create(chapterId, 'manual', '版本一', '手动保存')
+    expect(repo.list(chapterId)).toHaveLength(1)
+    expect(repo.list(chapterId)[0].name).toBe('手动保存')
+  })
+
+  it('prunes oldest auto snapshots', () => {
+    for (let i = 0; i < 5; i++) {
+      repo.create(chapterId, 'auto', `content-${i}`)
+    }
+    repo.pruneAuto(chapterId, 3)
+    const autos = repo.list(chapterId).filter((s) => s.type === 'auto')
+    expect(autos).toHaveLength(3)
+  })
+
+  it('restores snapshot content', () => {
+    const snap = repo.create(chapterId, 'manual', '可恢复内容')
+    expect(repo.restore(snap.id)).toBe('可恢复内容')
+  })
+})