refactor(api): merge review-queue into /api/activities, rename resolve to assign

Removes the unused GET /api/activities list/detail endpoints, moves the
review-queue list and resolve/unlock/unassign actions under
/api/activities, renames resolve to assign end-to-end, and drops the
now-unused store.ReviewQueue helper.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

backend/internal/api/server.go

@@ -350,7 +350,9 @@ func (s *Server) Router() http.Handler {
 
 				r.Route("/activities", func(r chi.Router) {
 					r.Get("/", s.handleListActivities)
-					r.Get("/{id}", s.handleGetActivity)
+					r.Post("/{activityID}/assign", s.handleAssignActivity)
+					r.Post("/{activityID}/unlock", s.handleUnlockActivity)
+					r.Post("/{activityID}/unassign", s.handleUnassignActivity)
 				})
 
 				r.Route("/workout-kinds", func(r chi.Router) {
@@ -361,13 +363,6 @@ func (s *Server) Router() http.Handler {
 
 				r.Post("/reclassify", s.handleReclassifyAll)
 
-				r.Route("/review-queue", func(r chi.Router) {
-					r.Get("/", s.handleReviewQueue)
-					r.Post("/{activityID}/resolve", s.handleResolveReview)
-					r.Post("/{activityID}/unlock", s.handleUnlockReview)
-					r.Post("/{activityID}/unassign", s.handleUnassignReview)
-				})
-
 				r.Get("/progression/{kindID}", s.handleProgression)
 			})
 		})