fix: bun.lock is gitignored — use package.json only for Docker cache

bun.lock is in .gitignore so it doesn't exist after checkout.
Dockerfile and workflows now use package.json only for deps caching.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

.github/workflows/ci-image.yml

@@ -8,14 +8,6 @@ on:
     branches: [main]
     paths:
       - '.github/docker/Dockerfile.ci'
-      - 'bun.lock'
-      - 'package.json'
-  # Build on PRs that change the image (so first PR run has it)
-  pull_request:
-    branches: [main]
-    paths:
-      - '.github/docker/Dockerfile.ci'
-      - 'bun.lock'
       - 'package.json'
   # Manual trigger
   workflow_dispatch:
@@ -30,7 +22,7 @@ jobs:
       - uses: actions/checkout@v4
 
       # Copy lockfile + package.json into Docker build context
-      - run: cp bun.lock package.json .github/docker/
+      - run: cp package.json .github/docker/
 
       - uses: docker/login-action@v3
         with: