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/schema.ts

@@ -172,3 +172,19 @@ export const sshCredentialUsage = sqliteTable("ssh_credential_usage", {
     .notNull()
     .default(sql`CURRENT_TIMESTAMP`),
 });
+
+export const snippets = sqliteTable("snippets", {
+  id: integer("id").primaryKey({ autoIncrement: true }),
+  userId: text("user_id")
+    .notNull()
+    .references(() => users.id),
+  name: text("name").notNull(),
+  content: text("content").notNull(),
+  description: text("description"),
+  createdAt: text("created_at")
+    .notNull()
+    .default(sql`CURRENT_TIMESTAMP`),
+  updatedAt: text("updated_at")
+    .notNull()
+    .default(sql`CURRENT_TIMESTAMP`),
+});