Add languages, user_names, users_public tables and routes; fix _se→_sv rename

- Fix broken rename migration array (sed had corrupted from values to _sv)
- Add languages table with status lifecycle and trilingual titles
- Add user_names table with unique lowercase index
- Add users_public table linking to user_names and languages (native/target)
- Wire all three new routes under /api/languages, /api/user-names, /api/users-public

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/routes/categories.js

@@ -53,11 +53,11 @@ router.get('/:id', async (req, res, next) => {
 // POST /api/categories
 router.post('/', async (req, res, next) => {
   try {
-    const { titel_de, titel_en, titel_se, difficulty_level } = req.body;
+    const { titel_de, titel_en, titel_sv, difficulty_level } = req.body;
     const result = await query(
-      `INSERT INTO categories (titel_de, titel_en, titel_se, difficulty_level, requested_at)
+      `INSERT INTO categories (titel_de, titel_en, titel_sv, difficulty_level, requested_at)
        VALUES ($1, $2, $3, $4, NOW()) RETURNING *`,
-      [titel_de || null, titel_en || null, titel_se || null, difficulty_level || null]
+      [titel_de || null, titel_en || null, titel_sv || null, difficulty_level || null]
     );
     res.status(201).json({ ...result.rows[0], word_ids: [] });
   } catch (err) { next(err); }
@@ -66,7 +66,7 @@ router.post('/', async (req, res, next) => {
 // PATCH /api/categories/:id
 router.patch('/:id', async (req, res, next) => {
   try {
-    const allowed = ['titel_de', 'titel_en', 'titel_se', 'status',
+    const allowed = ['titel_de', 'titel_en', 'titel_sv', 'status',
                      'difficulty_level', 'requested_at', 'published_at', 'blocked_at'];
     const fields = Object.keys(req.body).filter(k => allowed.includes(k));
     if (!fields.length) return res.status(400).json({ error: 'No valid fields provided' });