fix(review-2): critical — repair comment posting + close export data leak

CR1: the lightbox comment button POSTed to /upload/{id}/comment (singular);
     no such route exists, so every UI-submitted comment 404'd and was lost.
     Fixed to /comments (plural). The prior e2e passed because its seed helper
     POSTs the API directly — added comment-ui.spec.ts which drives the real
     component so this can't regress silently again.

CR2: export archives (Gallery.zip / Memories.zip / HTML viewer) were written
     under media_path, which is a public ServeDir — so GET /media/exports/
     Gallery.zip served the entire event (every photo, caption, comment,
     uploader name) to any anonymous visitor at a guessable URL, bypassing the
     ticket + release gate. Moved exports to a separate EXPORT_PATH (=/exports)
     on its own volume (Dockerfile chown, compose volume, gated handler reads
     the new path). export-leak.spec.ts asserts /media/exports/Gallery.zip → 404.

Riders (git can't split hunks): LightboxModal also gains H3 live-eviction on
comment-deleted/upload-deleted; config.rs also wires compression_concurrency
from boot config (medium).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

docker-compose.yml

@@ -34,6 +34,9 @@ services:
         condition: service_healthy
     volumes:
       - media_data:/media
+      # Export archives live OUTSIDE /media so the public media ServeDir can't
+      # serve them — downloads go only through the ticket-gated handler.
+      - exports_data:/exports
     expose:
       - "3000"
     healthcheck:
@@ -96,4 +99,5 @@ services:
 volumes:
   postgres_data:
   media_data:
+  exports_data:
   caddy_data: