Fix: Add Windows support for SQLite database access (Issue #23)

Replace CLI-based sqlite3 extraction with better-sqlite3 library:
- Create shared src/db/database.js module for cross-platform SQLite access
- Remove duplicate extractTokenFromDB functions from token-extractor.js and account-manager.js
- Add better-sqlite3 dependency with prebuilt Windows/Mac/Linux binaries
- Improve error handling with specific messages for common issues

Fixes #23

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

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

CLAUDE.md

@@ -58,6 +58,7 @@ Claude Code CLI → Express Server (server.js) → CloudCode Client → Antigrav
   - `thinking-utils.js` - Thinking block validation, filtering, reordering, and recovery logic
   - `signature-cache.js` - In-memory cache for Gemini thoughtSignatures
 - **src/account-manager.js**: Multi-account pool with sticky selection, rate limit handling, and automatic cooldown
+- **src/db/database.js**: Cross-platform SQLite database access using better-sqlite3 (Windows/Mac/Linux compatible)
 - **src/oauth.js**: Google OAuth implementation for adding accounts
 - **src/token-extractor.js**: Extracts tokens from local Antigravity app installation (legacy single-account mode)
 - **src/constants.js**: API endpoints, model mappings, OAuth config, and all configuration values