feat: add storage management features including user storage quota and usage tracking

- Updated database schema to include `storage_quota_bytes` and `plan` for users.
- Implemented storage usage calculations in `storageRepo` and added tests for storage functionality.
- Created `StorageManager` component to display and manage user storage.
- Enhanced user settings to show storage details and warnings for high usage.
- Added translations for new storage-related strings in English and Dutch.
- Updated styles for storage overview and details in CSS.

backend/src/db/migrations.ts

@@ -61,6 +61,16 @@ export function runMigrations(db: Database.Database): void {
     db.exec(`ALTER TABLE users ADD COLUMN role TEXT NOT NULL DEFAULT 'user'`);
   }
 
+  // ── Add storage_quota_bytes if missing ──
+  if (!cols.some((c) => c.name === "storage_quota_bytes")) {
+    db.exec(`ALTER TABLE users ADD COLUMN storage_quota_bytes INTEGER NOT NULL DEFAULT 1073741824`);
+  }
+
+  // ── Add plan if missing ──
+  if (!cols.some((c) => c.name === "plan")) {
+    db.exec(`ALTER TABLE users ADD COLUMN plan TEXT NOT NULL DEFAULT 'free'`);
+  }
+
   // ── Promote first user to admin if no admins exist ──
   const adminCount = db
     .prepare(`SELECT COUNT(*) AS cnt FROM users WHERE role = 'admin'`)