fix: image transforms via Sharp, model photos crash, video duration

- Backend: add Sharp image transform endpoint (/assets/:id?transform=X)
  with presets: mini(64), thumbnail(200), preview(480), medium(960), banner(1280)
  Transformed images are cached as webp next to originals
- Frontend: fix model photos crash (p.directus_files_id → p)
- Frontend: fix model banner URL (data.model.banner.id → data.model.banner)
- Frontend: fix video duration display (video.movie.duration → video.movie_file?.duration)
  across models/[slug], videos, videos/[slug], and home pages

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

Dockerfile.backend

@@ -18,8 +18,8 @@ COPY packages/buttplug/package.json ./packages/buttplug/package.json
 
 RUN pnpm install --frozen-lockfile --filter @sexy.pivoine.art/backend --ignore-scripts
 
-# Only rebuild the native argon2 binding — not buttplug or anything else
-RUN pnpm rebuild argon2
+# Rebuild native bindings (argon2, sharp)
+RUN pnpm rebuild argon2 sharp
 
 COPY packages/backend ./packages/backend
 
@@ -27,7 +27,7 @@ RUN pnpm --filter @sexy.pivoine.art/backend build
 
 RUN CI=true pnpm install --frozen-lockfile --filter @sexy.pivoine.art/backend --prod --ignore-scripts
 
-RUN pnpm rebuild argon2
+RUN pnpm rebuild argon2 sharp
 
 # ============================================================================
 # Runner stage