Add editable display title (was hardcoded to VITE_HOTEL_NAME)

New `config` table + routes/config.js: GET /api/public/config (no auth,
Display.tsx needs it with no session) and PUT /api/admin/config (authed +
'settings' cap). A blank title clears the override and falls back to the
build-time VITE_HOTEL_NAME, so an unconfigured install still shows
something sensible. Admin.tsx gets a "Display title" field above the
existing status card.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/src/db.js

@@ -48,8 +48,18 @@ export async function initDb() {
       sunset     TIMESTAMPTZ,
       fetched_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
     );
-  `)
 
+    -- User-editable display settings (currently just display_title). Separate from
+    -- the status table (fetch bookkeeping, not user-facing) -- same KV shape as
+    -- tasks' config table. A missing/null display_title falls back to
+    -- VITE_HOTEL_NAME at the frontend (see routes/config.js), so an unconfigured
+    -- app still shows something sensible without requiring a rebuild.
+    CREATE TABLE IF NOT EXISTS config (
+      key        TEXT PRIMARY KEY,
+      value      JSONB NOT NULL,
+      updated_at TIMESTAMPTZ NOT NULL DEFAULT NOW()
+    );
+  `)
 }
 
 export async function getStatus() {
@@ -64,3 +74,16 @@ export async function setStatus(key, value) {
     [key, JSON.stringify(value)]
   )
 }
+
+export async function getConfig() {
+  const { rows } = await pool.query('SELECT key, value FROM config')
+  return Object.fromEntries(rows.map(r => [r.key, r.value]))
+}
+
+export async function setConfigValue(key, value) {
+  await pool.query(
+    `INSERT INTO config (key, value, updated_at) VALUES ($1, $2, NOW())
+     ON CONFLICT (key) DO UPDATE SET value = EXCLUDED.value, updated_at = NOW()`,
+    [key, JSON.stringify(value)]
+  )
+}