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>

src/db/database.js

@@ -0,0 +1,93 @@
+/**
+ * SQLite Database Access Module
+ * Provides cross-platform database operations for Antigravity state.
+ *
+ * Uses better-sqlite3 for:
+ * - Windows compatibility (no CLI dependency)
+ * - Native performance
+ * - Synchronous API (simple error handling)
+ */
+
+import Database from 'better-sqlite3';
+import { ANTIGRAVITY_DB_PATH } from '../constants.js';
+
+/**
+ * Query Antigravity database for authentication status
+ * @param {string} [dbPath] - Optional custom database path
+ * @returns {Object} Parsed auth data with apiKey, email, name, etc.
+ * @throws {Error} If database doesn't exist, query fails, or no auth status found
+ */
+export function getAuthStatus(dbPath = ANTIGRAVITY_DB_PATH) {
+    let db;
+    try {
+        // Open database in read-only mode
+        db = new Database(dbPath, {
+            readonly: true,
+            fileMustExist: true
+        });
+
+        // Prepare and execute query
+        const stmt = db.prepare(
+            "SELECT value FROM ItemTable WHERE key = 'antigravityAuthStatus'"
+        );
+        const row = stmt.get();
+
+        if (!row || !row.value) {
+            throw new Error('No auth status found in database');
+        }
+
+        // Parse JSON value
+        const authData = JSON.parse(row.value);
+
+        if (!authData.apiKey) {
+            throw new Error('Auth data missing apiKey field');
+        }
+
+        return authData;
+    } catch (error) {
+        // Enhance error messages for common issues
+        if (error.code === 'SQLITE_CANTOPEN') {
+            throw new Error(
+                `Database not found at ${dbPath}. ` +
+                'Make sure Antigravity is installed and you are logged in.'
+            );
+        }
+        // Re-throw with context if not already our error
+        if (error.message.includes('No auth status') || error.message.includes('missing apiKey')) {
+            throw error;
+        }
+        throw new Error(`Failed to read Antigravity database: ${error.message}`);
+    } finally {
+        // Always close database connection
+        if (db) {
+            db.close();
+        }
+    }
+}
+
+/**
+ * Check if database exists and is accessible
+ * @param {string} [dbPath] - Optional custom database path
+ * @returns {boolean} True if database exists and can be opened
+ */
+export function isDatabaseAccessible(dbPath = ANTIGRAVITY_DB_PATH) {
+    let db;
+    try {
+        db = new Database(dbPath, {
+            readonly: true,
+            fileMustExist: true
+        });
+        return true;
+    } catch {
+        return false;
+    } finally {
+        if (db) {
+            db.close();
+        }
+    }
+}
+
+export default {
+    getAuthStatus,
+    isDatabaseAccessible
+};