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

auth/service_decorator.py

@@ -41,6 +41,8 @@ from auth.scopes import (
     SLIDES_READONLY_SCOPE,
     TASKS_SCOPE,
     TASKS_READONLY_SCOPE,
+    CONTACTS_SCOPE,
+    CONTACTS_READONLY_SCOPE,
     CUSTOM_SEARCH_SCOPE,
     SCRIPT_PROJECTS_SCOPE,
     SCRIPT_PROJECTS_READONLY_SCOPE,
@@ -388,6 +390,7 @@ SERVICE_CONFIGS = {
     "forms": {"service": "forms", "version": "v1"},
     "slides": {"service": "slides", "version": "v1"},
     "tasks": {"service": "tasks", "version": "v1"},
+    "people": {"service": "people", "version": "v1"},
     "customsearch": {"service": "customsearch", "version": "v1"},
     "script": {"service": "script", "version": "v1"},
 }
@@ -428,6 +431,9 @@ SCOPE_GROUPS = {
     # Tasks scopes
     "tasks": TASKS_SCOPE,
     "tasks_read": TASKS_READONLY_SCOPE,
+    # Contacts scopes
+    "contacts": CONTACTS_SCOPE,
+    "contacts_read": CONTACTS_READONLY_SCOPE,
     # Custom Search scope
     "customsearch": CUSTOM_SEARCH_SCOPE,
     # Apps Script scopes