Add Google Calendar connector (gcal)

- connector.json: OAuth Google, scope https://www.googleapis.com/auth/calendar
  deliver: file/google_authorized_user → {secrets}/google_creds.json
  mcp_config.env.GOOGLE_CREDS_PATH = {secrets}/google_creds.json
- verify.py: loads creds + API probe (calendarList.list)
- gcal_mcp_server.py: 8 tools (status, list_calendars, list_events,
  get_event, create_event, update_event, delete_event, respond_to_event)
  + push notification polling
- icons: calendar SVG (48px + 96px)
- connectors.json index: gcal entry with auth + sha256
- SKALD.md: tabella connector + stato verify aggiornati

connectors/gcal/icon_lg.svg

@@ -0,0 +1,7 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 96 96" width="96" height="96">
+  <rect x="8" y="16" width="80" height="72" rx="8" fill="#4285F4"/>
+  <rect x="8" y="16" width="80" height="16" rx="8" fill="#357AE8"/>
+  <rect x="18" y="4" width="8" height="16" rx="3" fill="#666"/>
+  <rect x="70" y="4" width="8" height="16" rx="3" fill="#666"/>
+  <text x="48" y="66" text-anchor="middle" font-family="sans-serif" font-size="36" font-weight="bold" fill="#fff">17</text>
+</svg>