Add Playwright e2e coverage + comment-level video upload workflow (#40)

## Summary
- add Playwright e2e auth setup + seeded test DB flow
- fix Playwright startup order so DB seed runs before web server uses SQLite
- add full trip-planning e2e scenario (future trip, travellers, destination, flight, lodging, upcoming verification)
- configure Auth.js custom sign-in page for base-path routing
- add repo guidance in AGENTS.md / CLAUDE.md requiring e2e for user-facing changes
- document and validate comment-level Gitea video attachment workflow (create comment, upload to comment assets endpoint)

## Validation
- bunx playwright test e2e/auth.test.ts --project=chromium\n- bunx playwright test e2e/trip-planning.test.ts --project=chromium
- PW_VIDEO_MODE=on PW_TRACE_MODE=off bunx playwright test e2e/trip-planning.test.ts --project=chromium

## Issue
- relates to #38

Co-authored-by: AI Agent <ai-agent@campbellwireless.net>
Reviewed-on: #40
Co-authored-by: Shaun Campbell <shaun@campbellwireless.net>
Co-committed-by: Shaun Campbell <shaun@campbellwireless.net>

.env.test

@@ -0,0 +1,21 @@
+# E2E test environment — used by the dev server during Playwright runs.
+# Never touches trips.db.
+
+AUTH_URL=http://127.0.0.1:5173/trips/auth
+AUTH_SECRET=e2e-test-secret-do-not-use-in-production-32b
+
+LOCAL_AUTH_ENABLED=true
+LOCAL_AUTH_ARGON2_MEMORY_KB=8192
+LOCAL_AUTH_ARGON2_TIME_COST=2
+LOCAL_AUTH_ARGON2_PARALLELISM=1
+
+# e2e_admin username is matched by isAdminUser() via DB lookup
+ADMIN_USER_IDS=e2e_admin
+
+# Separate test database — never touches trips.db
+DATABASE_URL=file:trips.test.db
+
+# Synology OIDC — not exercised in E2E tests but must be present to avoid startup errors
+SYNOLOGY_ISSUER=https://cloud.campbellwireless.net/auth/webman/sso
+SYNOLOGY_CLIENT_ID=e2e-placeholder
+SYNOLOGY_CLIENT_SECRET=e2e-placeholder