docs: add feedback widget for docs pages (fixes DOCSDEV-4)

[JonathanMatthey]

Description of changes

• Add a docs feedback widget in the footer.
• Add a Netlify function that creates GitHub issues for feedback.
• Add Netlify local dev config and docs for setup/testing.
• Add a local Netlify dev script and env example.
• Ignore local .netlify files.

Checklist

• PR title is prefixed with docs:
• PR title or description includes fixes #
• Run pnpm format and pnpm lint
• Review Vale output if applicable

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[melissahenderson]

Do you know if these issues will/can automatically create themselves in Linear? It's OK if not. The tech writers will plan accordingly.

[JonathanMatthey]

This wouldnt be part of this Feedback feature, but there is a way to achieve what you're looking for, through Linear

Auto-create Linear issues from GitHub feedback

as a Linear workspace admin.

Steps

1. In Linear, go to Settings → Integrations → GitHub and connect the interledger org (install/approve the Linear GitHub App, granting access to the interledger/open-payments-docs-feedback repo).
2. In the same GitHub integration panel, enable "Automatically create Linear issues from GitHub issues".
3. Configure the rule:
   • Repository: interledger/open-payments-docs-feedback
   • Label filter: feedback
   • Destination team: Docs (or whichever team should own this)
   • Default state: Triage (or equivalent)
4. Save.

Test

Open a test issue in interledger/open-payments-docs-feedback with the feedback label — a Linear issue should appear in the chosen team within a few seconds, linked back to the GitHub issue.