Task 357: CI Gate for Pages Deployment + Stats Refresh

Status: DONE

Description

The GitHub Pages deployment workflow (pages.yml) currently triggers independently of CI (ci.yml). This means a broken commit can be deployed to the live site even if CI fails. Add a CI gate so Pages only deploys after CI passes.

Also includes:

• Refresh stale stats in tech-overview.md (tasks: 355→357, tests: 2,949→current, commits: 496→current)
• Add a custom 404 page for better UX on invalid URLs

Changes

• .github/workflows/pages.yml: Use workflow_run trigger to deploy only after CI passes
• reports/data/summary/tech-overview.md: Refresh stats
• ts/src/templates.ts: Add 404.html generation
• ts/src/build.ts: Include 404.html in build output