Add build CI and automate fontdue-js bumps

[tomconroy]

Adds CI and automates the fontdue-js bump, so the release process no longer has to touch this repo by hand.

.github/workflows/build.yml — runs npm ci && npm run build on every PR and on main. This repo had no CI at all, so nothing verified that a new fontdue-js still compiles here. The release-time build was the only check, and it was manual.

.github/dependabot.yml — watches fontdue-js only, and bumps the exact pin in place rather than widening it to a range.

Automerge — the automerge job merges Dependabot's patch and minor bumps once build passes. needs: build is the gate; major bumps are left for a human, since those are the ones that break templates.

The build needs a reachable Fontdue backend, so the workflow points at the public staging URL (https://example.fontdue.xyz). No secrets required.

🤖 Generated with Claude Code

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