Add terminal snippets feature with sidebar UI (#377)

* Add terminal snippets feature with sidebar UI

- Add snippets CRUD API endpoints and database schema
- Implement snippets sidebar accessible from TopNavbar
- Add copy to clipboard functionality
- Include tooltips and optimized styling
- Add English and Chinese translations

* Update src/backend/database/routes/snippets.ts

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

---------

Co-authored-by: ZacharyZcR <zacharyzcr1984@gmail.com>
Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

src/backend/database/db/index.ts

@@ -242,6 +242,17 @@ async function initializeCompleteDatabase(): Promise<void> {
         FOREIGN KEY (user_id) REFERENCES users (id)
     );
 
+    CREATE TABLE IF NOT EXISTS snippets (
+        id INTEGER PRIMARY KEY AUTOINCREMENT,
+        user_id TEXT NOT NULL,
+        name TEXT NOT NULL,
+        content TEXT NOT NULL,
+        description TEXT,
+        created_at TEXT NOT NULL DEFAULT CURRENT_TIMESTAMP,
+        updated_at TEXT NOT NULL DEFAULT CURRENT_TIMESTAMP,
+        FOREIGN KEY (user_id) REFERENCES users (id)
+    );
+
 `);
 
   migrateSchema();