feat: AI fallback hardening + verified go-live gaps update #4085

Originally written by @ccantynz-alt on GitHub.
Imported from https://github.com/ccantynz-alt/AlecRae.com/pull/46

Summary

Follow-on launch-hardening that landed after PR #45 merged. Two commits:

• AI fallback hardening — translate / voice (draft + adjust) / voice-clone now degrade gracefully when ANTHROPIC_API_KEY is absent or the Claude call fails, instead of throwing a 500. Enforces the Bible rule "all AI calls must have fallback behaviour." Matches the existing fallback pattern in ai-writing.ts.
• Dunning tests — apps/api/tests/dunning.test.ts covers the failed-payment recovery state machine (active → past_due → active/downgraded).
• Preflight / load-test polish — final touches to scripts/preflight.ts and load-tests/.
• GO_LIVE_GAPS.md update — marks G1–G5/G8–G10 done, adds bundle/perf gaps P1–P5 from the static audit.

Verification (local)

• bun run lint — 0 errors (31 pre-existing console warnings)
• bun run typecheck — 37/37 packages
• bun run test — 61/61 (3× clean, no flakiness)

Audit corrections

• AI-fallback gaps were real → fixed here.
• The audit's "Outlook token refresh missing" was a false positive — refreshMicrosoftToken already exists and is correctly wired in sync/engine.ts (refreshes on expiry, persists rotated tokens). No change needed.

Not in scope (tracked in GO_LIVE_GAPS.md)

• P1–P5 bundle/perf work (Framer Motion on landing, three.js/yjs eager deps, bundle-size CI gate) — next tranche.
• G6 status-page live uptime wiring.

https://claude.ai/code/session_01CQjWseikSJdamHS8W6Kygz

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