ci: optimize workflows to cut redundant runs (#465)

* ci: optimize workflows to cut redundant runs and add timeout protection

Skip validation jobs (build, test, lint, Docker, E2E) on push-to-main
since code was already validated on the PR. Skip CI entirely for
release-please PRs (version bump only). Add timeout-minutes to all jobs
to prevent hung runners from burning 360 min (GitHub default). Add npm
caching to the start-app composite action. Add concurrency control to
docker-publish. Group Dependabot updates to batch PRs per ecosystem.

Estimated savings: ~10 min per release cycle, ~30-40 min/day.

* chore: add tsbuildinfo to gitignore

.github/workflows/docker-publish.yml

@@ -6,10 +6,15 @@ on:
       - 'v*'
   workflow_dispatch:
 
+concurrency:
+  group: docker-publish
+  cancel-in-progress: true
+
 jobs:
   push_to_registry:
     name: Push Docker image to Docker Hub
     runs-on: ubuntu-latest
+    timeout-minutes: 30
     steps:
       - name: Check out the repo
         uses: actions/checkout@v6