fix(ci): cancel superseded workflow runs to cut Actions minutes

[Copilot]

July consumed ~3513 Actions minutes, dominated by three workflows that fire on every PR push and merge: Pages (603 runs), Lint (501), E2E (360). E2E already cancels superseded runs via concurrency; the other three had none, so rapid re-pushes (Renovate automerge, bot/Copilot PRs) ran stale commits to completion.

Changes

• pages.yml — add concurrency keyed by github.ref, with cancellation scoped to pull_request so in-flight production deploys to main are never interrupted, only superseded PR preview builds:

  concurrency:
    group: pages-${{ github.ref }}
    cancel-in-progress: ${{ github.event_name == 'pull_request' }}

• lint.yml — add concurrency (group: lint-${{ github.ref }}, cancel-in-progress: true).
• links.yml — add concurrency (group: links-${{ github.ref }}, cancel-in-progress: true); scheduled and PR runs use distinct refs, so the weekly link-rot job is unaffected.

Notes

• Per-ref grouping isolates main from PR refs; no run type is dropped, only superseded duplicates are cancelled.
• Mirrors the existing pattern in e2e.yml; no application code touched.

• Fixes fix(ci): reduce workflow usage #173