feat: review queue polish (pace, sort, type filter), drop unused phase-detection UI

Review Queue: show pace alongside distance/duration/HR, sort by activity
date (most recent first) instead of classification timestamp, and add a
filter by workout kind with a special "Unsorted" option for runs where
the rule engine found zero candidates at all (distinct from ambiguous
multi-candidate runs).

Profile: remove the phase-detection warm-up/cool-down section from the
UI -- not used by anything yet (phase segmentation is future work) and
was adding noise. The underlying fields are untouched so no data is lost
and the settings screen still round-trips them on save.

backend/internal/api/review.go

@@ -3,6 +3,7 @@ package api
 import (
 	"encoding/json"
 	"net/http"
+	"sort"
 	"strconv"
 
 	"github.com/go-chi/chi/v5"
@@ -33,6 +34,13 @@ func (s *Server) handleReviewQueue(w http.ResponseWriter, r *http.Request) {
 		}
 		items = append(items, item{KindAssignment: a, Activity: activity})
 	}
+
+	// Most recent run first, by when the activity actually happened (not
+	// when the rule engine flagged it), so the queue reads like a log.
+	sort.Slice(items, func(i, j int) bool {
+		return items[i].Activity.StartTimeUTC > items[j].Activity.StartTimeUTC
+	})
+
 	writeJSON(w, http.StatusOK, items)
 }