Use cancel-in-progress for GitHub Pages deployments to prevent unbounded growth

[Copilot]

Each push to main creates a new GitHub Pages deployment entry. With cancel-in-progress: false, concurrent pushes queue independently, causing the deployment list to grow indefinitely rather than reflecting only the current live state.

Change

• Set cancel-in-progress: true in the docs.yml concurrency block so a newer push cancels any in-flight deployment instead of queuing behind it

# .github/workflows/docs.yml
concurrency:
  group: "pages"
  cancel-in-progress: true  # was: false

Cancelled runs still appear in history but are marked cancelled, keeping the set of active/successful deployments bounded to the latest state.

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