List Google calendars and choose the one to push to (Feature 16)

GET /api/v1/integrations/google/calendars trades the stored refresh token
for an access token, reads every calendarList page and answers
[{id, summary, primary, accessRole}] for writer and owner calendars only.
PUT /api/v1/integrations/google/calendar {calendar_id} validates the id
against that same filtered listing and stores calendar_id and
calendar_name; any other id is 422 unknown_calendar.

Both hold the service's account lock, answer 409 not_connected with
nothing connected, and 502 reconnect_required when Google no longer
accepts the grant, leaving the connection as it is. The gcaltest fake
gains the refresh grant and a pausable calendarList endpoint.

Maestro task 0fe3f1f2-4932-4d10-81dd-74c4f630d215.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/server/server.go

@@ -47,7 +47,8 @@ type RouteMounter interface {
 // /api/v1/plans/{weekStart}/draft, PUT
 // /api/v1/plans/{weekStart}/days/{date}, GET /api/v1/rotation-reviews and
 // POST /api/v1/dinners/{id}/rotation-review; googleSvc serves GET
-// /api/v1/integrations/google/connect and /callback and DELETE
+// /api/v1/integrations/google/connect, /callback and /calendars, PUT
+// /api/v1/integrations/google/calendar and DELETE
 // /api/v1/integrations/google; runner serves
 // POST /api/v1/jobs and GET /api/v1/jobs/{id}; photos serves
 // GET /media/photos/{id}-{size}.jpg; assets is the web build
@@ -140,6 +141,8 @@ func NewRouter(logger *slog.Logger, version string, trusted forwarded.Trusted, a
 	apiV1.Get("/integrations/google/connect", getGoogleConnect(logger, googleSvc))
 	apiV1.Get("/integrations/google/callback", getGoogleCallback(logger, googleSvc))
 	apiV1.Delete("/integrations/google", deleteGoogle(logger, googleSvc))
+	apiV1.Get("/integrations/google/calendars", getGoogleCalendars(logger, googleSvc))
+	apiV1.Put("/integrations/google/calendar", putGoogleCalendar(logger, googleSvc))
 	apiV1.Post("/jobs", postJob(logger, runner))
 	apiV1.Get("/jobs/{id}", getJob(logger, runner))
 	media.Get("/photos/{name}", getPhoto(logger, photos))