docs: document staging and release-tag prod deploys

[balebbae]

Summary

Deploys changed. A merge to main now deploys staging (harp-staging), and prod (harp) deploys only when a release tag is pushed. Merging the release-please PR creates that tag. The docs still said a merge to main deploys prod. This PR updates them and documents the staging setup.

Changes

.claude/skills/deployment/SKILL.md

• Prod vs staging services: URLs, what triggers each deploy, and their ENV values.
• The two Cloud Build triggers. Their build config must stay inline, because switching to Autodetected or Repository breaks the deploy.
• What happens on a merge to main vs Releasing to prod: urgent fixes, and redeploying an existing tag.
• New Staging section:
  • each piece side by side with prod: Neon branch, SuperTokens dev instance, Mailtrap, VAPID keys, bucket, OAuth client, STAGING_* secrets, scoped service account, Cloudflare Access
  • what ENV=staging changes in the code (the re-link from feat(auth): relink users by email on staging #187)
• Keep staging from reaching real people: no SendGrid, never prod's VAPID keys, bucket or SuperTokens, and why each one matters.
• Access gaps (the run.app URL, ACM's shared seat limit) and how to sign in on staging.
• Refreshing staging's data with neon branches reset staging --parent.
• Migrations: apply to staging before merging the PR and to prod before merging the release PR, using Neon's direct URLs. Destructive changes now take two releases.
• Rollback with the real service and region names. A revert on main now only reaches staging.
• New symptom rows: "merged but not in prod", the staging re-link error, the Mailtrap cap, Access seats.

.claude/skills/ci-pipeline/SKILL.md

• Separate staging and prod deploy rows.
• The change flow now ends with merging the release PR.
• The release section says the tag deploys prod.
• Quick answers updated, plus a new "When does my change reach prod?"

claude.md

• The CD bullet covers both triggers.
• New Staging and Migrations bullets.
• Neon branches and the email provider for each environment.

.github/workflows/migration-reminder.yaml

• The PR comment says to apply migrations to staging before merging and to prod before releasing, instead of "merging deploys the code".

Docs and comment text only. No code or config changes.

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