Fix site settings schedule and session handling - #66

Summary

• Add schedule deletion support through the sites API.
• Update the site settings UI so deleted schedules disappear immediately and do not reappear from stale cache data.
• Sanitize regression alert update payloads before saving and add visible success/error feedback.
• Harden server-side session resolution for production web starts by using an absolute API URL and Cookie header fallback.

Root cause

Schedule deletion did not have a dedicated API endpoint, and the UI could keep stale schedule data after mutation/refetch. Regression alert updates also sent fields not accepted by the update API. Separately, SSR session loading could fail in production when the server attempted to resolve sessions using a relative API URL or missed the refresh token through the helper cookie lookup.

Validation

• pnpm --filter web test -- src/lib/session-server.test.ts src/lib/site-settings-payloads.test.ts
• pnpm --filter web typecheck
• pnpm --filter web build
• pnpm --filter server test -- src/sites/sites.controller.spec.ts src/sites/sites.service.spec.ts
• Push hook: pnpm format:check && pnpm lint && pnpm typecheck && pnpm test && pnpm build