feat: Add folder customization and batch delete for SSH host manager

Allow users to customize folder appearance and manage hosts in bulk:

Database & Types:
- Add sshFolders table with color and icon fields for folder metadata
- Add SSHFolder interface to types with userId, name, color, icon fields
- Update folder rename route to also update folder metadata

API Endpoints:
- GET /ssh/folders - Fetch all folders with metadata for user
- PUT /ssh/folders/metadata - Create or update folder color and icon
- DELETE /ssh/folders/:name/hosts - Delete all hosts in a folder and folder metadata

Frontend Features:
- Create FolderEditDialog component with color picker (8 colors) and icon selector (10 icons)
- Add folder metadata state management in HostManagerViewer
- Display custom folder colors and icons in host manager UI
- Add "Edit Folder Appearance" button with palette icon
- Add "Delete All Hosts in Folder" button with trash icon and confirmation
- Fetch and sync folder metadata on component mount and refresh

API Functions:
- getSSHFolders() - Retrieve all folder metadata
- updateFolderMetadata(name, color, icon) - Update folder appearance
- deleteAllHostsInFolder(folderName) - Batch delete with count return

i18n Support:
- Add translations for folder customization (en, zh)
- Add batch delete confirmation messages
- Add success/error toast messages

src/backend/database/db/schema.ts

@@ -209,6 +209,22 @@ export const snippets = sqliteTable("snippets", {
     .default(sql`CURRENT_TIMESTAMP`),
 });
 
+export const sshFolders = sqliteTable("ssh_folders", {
+  id: integer("id").primaryKey({ autoIncrement: true }),
+  userId: text("user_id")
+    .notNull()
+    .references(() => users.id),
+  name: text("name").notNull(),
+  color: text("color"),
+  icon: text("icon"),
+  createdAt: text("created_at")
+    .notNull()
+    .default(sql`CURRENT_TIMESTAMP`),
+  updatedAt: text("updated_at")
+    .notNull()
+    .default(sql`CURRENT_TIMESTAMP`),
+});
+
 export const recentActivity = sqliteTable("recent_activity", {
   id: integer("id").primaryKey({ autoIncrement: true }),
   userId: text("user_id")