contacts: extract into standalone skill, add himalaya wrapper for all email sends

Refactors the contacts system from being embedded in cal_tool.py into a
standalone contacts skill that serves as the single source of truth for
recipient validation across all outbound email paths.

- New skills/contacts/ skill: list, add, delete, resolve commands
- New skills/himalaya/scripts/himalaya.sh wrapper: validates To/Cc/Bcc
  recipients against contacts for message send, template send, and
  message write commands; passes everything else through unchanged
- cal_tool.py now delegates to contacts.py resolve instead of inline logic
- TOOLS.md updated: agent should use himalaya wrapper, not raw himalaya

skills/calendar/scripts/calendar.sh

@@ -4,12 +4,9 @@
 # Usage:
 #   ./calendar.sh send [options]          # send a calendar invite (supports --rrule)
 #   ./calendar.sh reply [options]         # accept/decline/tentative
-#   ./calendar.sh event list [options]      # list/search calendar events
-#   ./calendar.sh event delete [options]    # delete an event by UID or summary
-#   ./calendar.sh contact list              # list all contacts
-#   ./calendar.sh contact add [options]     # add a contact
-#   ./calendar.sh contact delete [options]  # delete a contact
-#   ./calendar.sh todo add [options]        # create a todo
+#   ./calendar.sh event list [options]    # list/search calendar events
+#   ./calendar.sh event delete [options]  # delete an event by UID or summary
+#   ./calendar.sh todo add [options]      # create a todo
 #   ./calendar.sh todo list [options]     # list pending todos
 #   ./calendar.sh todo edit [options]     # edit a todo's fields
 #   ./calendar.sh todo complete [options] # mark todo as done