Summary

• add a core reset API that clears a book's reading sessions and resets its saved progress/current CFI
• create reading-session tombstones when clearing stats so sync can propagate the reset
• expose resetBookReadingData in desktop/mobile library stores
• add a mobile book action sheet entry to reset reading data without deleting the book, notes, highlights, or bookmarks

Notes

• Issue 建议优化阅读字数统计的逻辑 #336 also mentions drag-seek word count accuracy. Current reader progress sliders already suppress reading-stat accumulation during seek/programmatic navigation; this PR focuses on the missing per-book reset action requested in the issue.

Verification

• pnpm --filter @readany/core test -- session-queries book-queries
• pnpm --filter app exec tsc --noEmit
• pnpm --filter @readany/app-expo exec tsc --noEmit
• pnpm exec biome check packages/core/src/db/session-queries.ts packages/core/src/db/book-queries.ts packages/core/src/db/database.ts packages/core/src/db/index.ts packages/core/src/db/tests/session-queries.test.ts packages/core/src/db/tests/book-queries.test.ts packages/app-expo/src/components/library/BookCardActionSheet.tsx
• git diff --check

Fixes #336