fix: resolve issues #194, #195, #196, #197

[the-luap]

Summary

Backport of #198 (beta) — fixes for four reported GitHub issues:

• [BUG] Can't send Invite Link: Failed to parse date format setting. #194 - Date format parsing bug: Frontend was sending only the format string (e.g. "DD/MM/YYYY") instead of the full { format, locale } object when saving date format settings. The backend then failed to JSON.parse the bare string.
• [BUG] Forgot password & Others #195 - Multiple issues: Removed the non-functional "Forgot password" placeholder link (href="#"). Fixed README port from 3005 to 3000.
• [QUESTION] ADMIN PASSWORD #196 - ADMIN_PASSWORD not working: The migration now respects ADMIN_PASSWORD from env instead of always generating a random password. Also create-admin.js now updates the existing user's password instead of failing silently when the user already exists.
• [BUG] Feedback-filtering does not work #197 - Feedback filter export bug: Photo export was sending camelCase filter keys (minRating, hasLikes, etc.) but the backend PhotoFilterBuilder expects snake_case (min_rating, has_likes). Filters were silently ignored, exporting all photos instead of filtered ones.

Closes #194, closes #197

Changed files

File	Change
frontend/src/features/settings/hooks/useSettingsState.ts	Send full date_format object
frontend/src/pages/admin/AdminLoginPage.tsx	Remove broken forgot password link
frontend/src/components/admin/PhotoExportMenu.tsx	Convert filter keys to snake_case
backend/migrations/core/001_init.js	Use ADMIN_PASSWORD env var
backend/scripts/create-admin.js	Update existing user instead of erroring
README.md	Fix port 3005 → 3000

Test plan

• Change date format in settings, verify no backend JSON parse errors
• Verify admin login page no longer shows broken "Forgot password?" link
• Set ADMIN_PASSWORD in .env, fresh docker compose up → verify login works
• Apply feedback filters, export filename list → verify only filtered photos exported