fix: scrub raw error messages from error boundary before display

[advikdivekar]

Summary

Closes #452

error.tsx rendered error.message directly inside a <code> block with no sanitisation. Any runtime error — Supabase constraint violations,
console.error(error) also fired unconditionally in the browser, including in production.

Changes

• getSafeMessage(error) — new helper that:
  • Maps known error types (e.g. TokenRevoked) to user-friendly copy via SAFE_ERROR_MESSAGES
  • Returns a generic "An unexpected error occurred. Our team has been notified." in production for all other errors
  • Returns the raw message only in development (useful for debugging)
• Raw <code> block removed — error.message is no longer rendered in JSX; only getSafeMessage(error) is
• error.digest surfaced — shown as "Error ID" when present, so support can correlate without leaking internals
• console.error gated — only fires in non-production; a reportToSentry(error) hook comment is left for wiring up real error reporting

Test plan

• Production mode: Supabase error "supabaseUrl is required." → shows generic message, not raw text
• Production mode: DB constraint error "duplicate key value violates unique constraint '...'" → shows generic message
• Production mode: TokenRevoked error → shows "Your GitHub session has expired. Please sign in again."
• Development mode: TokenRevoked → same user-friendly mapping applies
• Development mode: raw error message shown (debugging intact)
• error.digest shown as Error ID when present (allows support correlation)
• console.error not called in production (verified by gating on NODE_ENV !== "production")
• npm run lint and npm run type-check pass with zero errors

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[github-actions]

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