Harden feedback comments and voting UX

[woolfg]

Summary

• validate and normalize feedback episode IDs, vote types, comments, emails, and user agents before DB writes
• replace vote REPLACE INTO with duplicate-key updates
• improve feedback/comment templates with responsive layout, labels, focus states, preserved invalid input, and inline form errors
• add unit coverage for feedback edge cases

Tests

• npm test -- FeedbackApi.test.ts
• npm run build