[codex] Add custom open-to-work contact email

[B-EtterDigital]

Summary

• Add an optional custom contact email to open-to-work profiles.
• Validate/normalize the email in a shared helper and API route.
• Store the email in a nullable profiles.open_to_work_email column and clear it when opting out.
• Show email contact actions on /hire when an opted-in engineer has saved an email, falling back to GitHub contact otherwise.
• Harden mailto: links against query/header injection and encode mailto components.
• Add an accessible label to the owner contact email input.

Migration

• Adds supabase/migrations/005_open_to_work_email.sql with nullable open_to_work_email, an email-format check constraint, and a DB invariant that email is only stored when open_to_work is true.
• supabase db push was attempted locally but blocked because this checkout is not linked to a Supabase project ref: Cannot find project ref. Have you run supabase link?

Validation

• pnpm test passes on this branch: 19 ccusage tests and 9 open-to-work tests.
• Combined merge simulation for PRs [codex] Fix leaderboard sorting, timelines, and duplicate claims #72, [codex] Add expandable profile model list #73, [codex] Make profile rank more prominent #74, [codex] Add custom open-to-work contact email #75 passes pnpm test: 19 ccusage + 9 open-to-work + 10 model-list + 6 rank + 19 site-bug tests.
• Combined production build passes in a temp worktree with dummy auth/Supabase env values.
• git diff --check passes.

Scope

Feature-only PR. It intentionally does not include PR #72 bug fixes, PR #73 expandable model list changes, or PR #74 rank presentation changes.

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