Fix seeder: origin mismatch + robust Dockerfile

Two root causes for seeding not working on production:

1. Origin mismatch: The seeder writes content IDs as
   http://localhost:7777/content/... but the app was using
   window.location.origin (the user's actual browser URL) to
   query the relay. Introduced VITE_CONTENT_ORIGIN env var
   baked into the Docker build so both sides use the same origin.

2. Dockerfile.seed fragility: Replaced --omit=dev + global tsx
   with a cleaner approach that strips sharp from package.json
   (the only native dep that fails on Alpine) then does a full
   npm install, ensuring tsx/esbuild and all applesauce deps
   resolve correctly.

Also improved wait-for-relay to accept any HTTP response (some
relays return 4xx for plain GET) and increased max attempts.

Co-authored-by: Cursor <cursoragent@cursor.com>

Dockerfile

@@ -20,6 +20,10 @@ ENV VITE_NOSTR_RELAYS=""
 # so auth and content use built-in mock/local data instead of timing out
 ENV VITE_USE_MOCK_DATA=true
 
+# Content origin must match the seeder's ORIGIN so that relay queries find
+# the seeded data, regardless of how users access the app in their browser
+ENV VITE_CONTENT_ORIGIN=http://localhost:7777
+
 # Build the application
 RUN npm run build