Contacts management page + MySQL-only backend

- vm_contacts: mysql-only backend (removed file/google/carddav from _BACKENDS)
- contacts.conf: backends=mysql (no fallback)
- vm_web.py: /contacts CRUD list (list, new, edit, delete, delete_all)
- vm_web.py: /contacts/import_vcf re-imports from VCF (skips junk names)
- nav: Contacts link added for authenticated users
- fixes: _MySQLCon.__iter__ for get_settings loop; add_contact row.id check

src/vm_contacts.py

@@ -2,11 +2,9 @@
 """
 Caller-ID -> contact name resolution for Asterisk voicemail notifications.
 
-Backends (tried in the order given by contacts.conf 'backends='):
+Backends (contacts are resolved exclusively from the MySQL `contacts` table
+on the asterisk DB):
   mysql   - MySQL contacts table on the asterisk DB (primary, fast, offline).
-  file    - local vCard (.vcf) or CSV export; no auth, offline, fast.
-  google  - Google People API via the Hermes OAuth token.
-  carddav - generic CardDAV with username + app password.
 
 Everything here is best-effort: a lookup failure returns None and the caller
 falls back to the raw caller-ID string.  Results (hits AND misses) are cached
@@ -393,7 +391,7 @@ def lookup_carddav(cfg, num_digits, n, log):
 
 
 # ---------------------------------------------------------------- entrypoint
-_BACKENDS = {"mysql": lookup_mysql, "file": lookup_file, "google": lookup_google, "carddav": lookup_carddav}
+_BACKENDS = {"mysql": lookup_mysql}
 
 
 def resolve(caller_id, log=print):