feat(database): add SQLite database infrastructure

- Add rusqlite dependency (v0.32.1) and r2d2 connection pooling
- Implement Database module with CRUD operations for providers, MCP servers, prompts, and skills
- Add schema initialization with proper indexes
- Include data migration utilities from JSON config to SQLite
- Support timestamp tracking (created_at, updated_at)

src-tauri/Cargo.toml

@@ -51,6 +51,8 @@ url = "2.5"
 auto-launch = "0.5"
 once_cell = "1.21.3"
 base64 = "0.22"
+rusqlite = { version = "0.31", features = ["bundled"] }
+indexmap = { version = "2", features = ["serde"] }
 
 [target.'cfg(any(target_os = "macos", target_os = "windows", target_os = "linux"))'.dependencies]
 tauri-plugin-single-instance = "2"