feat: add Google Contacts (People API) support

Add 16 MCP tools for managing Google Contacts via the People API:

Core tier:
- list_contacts, get_contact, search_contacts, create_contact

Extended tier:
- update_contact, delete_contact, list_contact_groups, get_contact_group

Complete tier:
- batch_create_contacts, batch_update_contacts, batch_delete_contacts
- create_contact_group, update_contact_group, delete_contact_group
- modify_contact_group_members

Includes:
- OAuth scopes for contacts and contacts.readonly
- People API service configuration
- Tool tier definitions
- Unit tests for helper functions

core/tool_tiers.yaml

@@ -138,6 +138,26 @@ tasks:
     - move_task
     - clear_completed_tasks
 
+contacts:
+  core:
+    - search_contacts
+    - get_contact
+    - list_contacts
+    - create_contact
+  extended:
+    - update_contact
+    - delete_contact
+    - list_contact_groups
+    - get_contact_group
+  complete:
+    - batch_create_contacts
+    - batch_update_contacts
+    - batch_delete_contacts
+    - create_contact_group
+    - update_contact_group
+    - delete_contact_group
+    - modify_contact_group_members
+
 search:
   core:
     - search_custom