feat(digitalocean): guided readiness before deploy

[scott]

Summary

Goal: Run a guided readiness check before region/size and Droplet creation so users fix account issues early and avoid failed or wasteful deploys.

What changed

• Pre-flight gate (DO only): After cloud auth, ensureReadyBeforeSizing runs evaluateDigitalOceanReadiness (account snapshot via GET /v2/account, SSH on DO, OpenRouter key, droplet limit). Blockers are fixed in order; payment-related account state is handled before SSH registration (DO often blocks keys until billing is OK).
• Checklist UI: Clear READY / BLOCKED / not checked yet, one guided step at a time; re-check after browser or token fixes until READY.
• Billing: Detect locked/warning account status up front; deep link to add payment (…billing?defer-onboarding-for=or&open-add-payment-method=true); shared handleBillingError path.
• Orchestration: Readiness runs before sizing so fast/parallel paths don’t boot while the account is still blocked.
• Non-interactive: Fail fast; optional --json-readiness / SPAWN_JSON_READINESS with SPAWN_NON_INTERACTIVE=1.
• DO OAuth: After 120s, interactive sessions keep waiting (or Escape → manual token); non-interactive still fails at 120s.
• Also: Exported verifyOpenRouterApiKey, DO helpers/tests, reset-local-state.sh, and DO README updates.

How to test

• Interactive: incomplete account → checklist → READY → then region/size.
• Billing: warning / no card → deep link → return → re-check.
• CI-style: SPAWN_NON_INTERACTIVE=1 → clean exit + JSON if enabled.

Other clouds unchanged.