PT-03: Make UMBRA_URL configurable via env var (default http://localhost).
Replaces hardcoded http://10.0.69.35 in notification dispatch job and
ntfy test endpoint. Add UMBRA_URL to .env.example.
PT-05: Add explicit path="/" to session cookie for clarity.
PT-06: Add concurrent session limit (MAX_SESSIONS_PER_USER, default 10).
When exceeded, oldest sessions are revoked. New login always succeeds.
PT-07: Escape LIKE metacharacters (%, _) in admin audit log action
filter to prevent wildcard abuse.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>