fix: unique, chronologically sortable result filenames

Two badges of the same person, same format, same day produced the same
filename -- `2026-07-23_lea_the-frame.png` -- and the second upload silently
overwrote the first at Picdrop. The name now carries the time down to the
second and a short tag derived from the item id:

  2026-08-20_143207_lea-badge_the-frame_a3f9.jpg

The timestamp leads, so any file listing sorts chronologically on its own.
The tag is derived, not random, so re-running the backfill is idempotent.
Timestamps use Europe/Berlin (KLARBILD_TZ) rather than UTC -- a picture taken
at 00:30 should not be dated to the previous day.

Naming moved into its own dependency-free module so the rules are testable and
identical everywhere. The generator strips its own stamp when a result is fed
back in as a source, so names cannot accumulate.

Backfill for the existing library in Admin -> Dateinamen: preview first, then
apply. It re-stamps from `created_at` and the item id, keeping the motif and
format already chosen, and leaves the stored files alone -- they live under
their id, not their name. A separate button re-delivers everything under the
new name; the old copies stay put at the destination, since deleting a
customer's files automatically is the wrong reflex.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BNhLunz586g6DeYMa7Qsd1

src/pages/api/admin/storage.ts

@@ -1,5 +1,6 @@
 import type { APIRoute } from 'astro';
 import { storageStats, runRetention, purgeSources, mirrorAllToNas, rebuildThumbs } from '../../../lib/maintenance';
+import { renameLibrary, redeliverAll } from '../../../lib/renames';
 import { one } from '../../../lib/db';
 
 export const prerender = false;
@@ -8,12 +9,16 @@ const json = (b: unknown, s = 200) =>
 
 export const GET: APIRoute = async () => json({ stats: await storageStats() });
 
-// POST { action: 'retention' | 'purge_sources' }
+// POST { action: 'retention' | 'purge_sources' | 'rename_preview' | 'rename_apply' | 'redeliver_all' | … }
 export const POST: APIRoute = async ({ request }) => {
   const b = await request.json().catch(() => ({}));
   if (b.action === 'purge_sources') return json(await purgeSources());
   if (b.action === 'mirror_all') return json(await mirrorAllToNas());
   if (b.action === 'rebuild_thumbs') return json(await rebuildThumbs());
+  // Eindeutige Dateinamen: erst zeigen, was passieren würde, dann anwenden.
+  if (b.action === 'rename_preview') return json(await renameLibrary(true));
+  if (b.action === 'rename_apply') return json(await renameLibrary(false));
+  if (b.action === 'redeliver_all') return json(await redeliverAll());
   if (b.action === 'retention') {
     const s = await one<{ retention_days: number | null }>('SELECT retention_days FROM settings WHERE id=1');
     if (!s?.retention_days) return json({ error: 'Keine Aufbewahrungsfrist gesetzt.' }, 400);