Add contacts/phone book system with per-user scoping

New files:
- lib/auth.py: Authentik forward-auth helpers (get_user_id, @require_auth)
- lib/contacts.py: ContactsDB with CRUD, soft delete, restore, purge, find_nearby
- lib/contacts_api.py: Flask Blueprint with 9 API endpoints at /api/contacts
- templates/knowledge/deleted_contacts.html: Dashboard recovery page

Modified:
- lib/api.py: Register contacts_bp, add KNOWLEDGE_SUBNAV entry, /deleted-contacts route
- config/profiles: has_contacts feature flag (true for home, false for pi profiles)

Separate SQLite DB at data/contacts.db. Per-user isolation via X-Authentik-Username.
Home/Work labels enforced unique per user. Haversine proximity queries (75m default).

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

config/profiles/regional_pi.yaml

@@ -41,6 +41,7 @@ features:
   has_address_book_write: true
   has_overture_enrichment: false
   has_google_places_enrichment: false
+  has_contacts: false
 
 defaults:
   center: [44.0, -114.0]