Add KeyValidation module for format-checking API keys before
attempting connections. Auto-strips whitespace, detects common
mistakes (e.g. pasting a Stripe publishable key), and returns
helpful error messages.
Inline field errors across all three entry points:
- Setup wizard: provider + Stripe keys
- Admin provider form: simplified to single Connect button
- Email settings: per-field errors instead of flash toasts
Also: plain text inputs for all API keys (not password fields),
accessible error states (aria-invalid, role=alert, thick border,
bold text), inner_block slot declaration on error component.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>