Fix seeder: skip heavy devDeps, decouple app from seeder success

- Use npm ci --omit=dev to avoid building sharp (needs native libvips
  not available on Alpine) then install tsx separately
- Change app depends_on from seeder (service_completed_successfully)
  to relay only, so the app still starts even if seeding fails

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

Dockerfile.seed

@@ -7,9 +7,10 @@ FROM node:20-alpine
 
 WORKDIR /app
 
-# Install dependencies (need full install so tsx/esbuild get their binaries)
+# Install only production deps (skip sharp & other heavy devDeps),
+# then add tsx separately so we can run TypeScript seed scripts.
 COPY package*.json ./
-RUN npm ci
+RUN npm ci --omit=dev && npm install --no-save tsx
 
 # Copy only what the seed scripts need
 COPY scripts/ ./scripts/