feat: custom formats (WxH/stickerN), JPG output option, failed-job status

- format.ts parses free formats from the key: sticker<N> -> N×N cm,
  <W>x<H> -> W×H cm. Fixes 'Unbekanntes Format: sticker5' (the seeded
  'Sticker 5 cm' recipe was unusable) and lets admins define ANY format
  without a migration. Guarded to <=300 cm.
- Output file format PNG/JPG: global default (settings.output_ext) plus
  per-recipe/per-conversion override. JPG only for non-alpha; cutouts
  stay PNG. file.ts sniffs content-type from magic bytes.
- Jobs can now be 'failed' (all items failed) -> red in the queue; add
  finished time to queue list + detail. migration 012.
- Studio: custom-measure input + Dateiformat selector; Admin: global
  Standard-Dateiformat.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XNQ8ghPfzAfsyVYd6HgFb6

src/pages/api/admin/settings.ts

@@ -25,6 +25,7 @@ export const GET: APIRoute = async () => {
     keep_sources: s.keep_sources, make_thumbnails: s.make_thumbnails, retention_days: s.retention_days,
     metadata_sidecar: s.metadata_sidecar, api_token: s.api_token,
     picdrop_metadata_sidecar: s.picdrop_metadata_sidecar, nas_metadata_sidecar: s.nas_metadata_sidecar,
+    output_ext: s.output_ext,
     // Rechte / Datenschutz / NSFW
     library_visibility: s.library_visibility, anonymous_generations: s.anonymous_generations,
     private_allowed: s.private_allowed, allow_nsfw: s.allow_nsfw,
@@ -48,7 +49,7 @@ export const PATCH: APIRoute = async ({ request }) => {
   for (const col of ['picdrop_host', 'picdrop_protocol', 'picdrop_port', 'picdrop_user', 'picdrop_base_path',
     'picdrop_default_gallery', 'default_dpi', 'default_crop_mode', 'concurrency', 'cricut_sheet_cm', 'monthly_budget', 'n8n_webhook_url',
     'keep_sources', 'make_thumbnails', 'retention_days', 'metadata_sidecar', 'api_token',
-    'picdrop_metadata_sidecar', 'nas_metadata_sidecar',
+    'picdrop_metadata_sidecar', 'nas_metadata_sidecar', 'output_ext',
     'library_visibility', 'anonymous_generations', 'private_allowed', 'allow_nsfw',
     'nas_enabled', 'nas_host', 'nas_protocol', 'nas_port', 'nas_user', 'nas_base_path']) {
     if (col in b) {