Replace per-kind reclassify with a single global reclassify that respects manual and Race locks

Manual assignments are the user's definitive word and Race assignments come
from a hard Garmin fact (eventType.typeKey), not a retunable rule -- neither
is ever touched by reclassify again, and Race can no longer be set by hand
via the review queue. Adds an Activities page so this locked/unlocked status
is visible per workout, since Review Queue only ever showed unresolved items.

backend/internal/store/assignments.go

@@ -83,6 +83,27 @@ func (db *DB) ReviewQueue(ctx context.Context) ([]KindAssignment, error) {
 	return assignments, rows.Err()
 }
 
+// AllCurrentAssignments returns the latest assignment for every activity
+// that has one, regardless of status or source -- the basis for deciding
+// which activities a global reclassify pass is allowed to touch.
+func (db *DB) AllCurrentAssignments(ctx context.Context) ([]KindAssignment, error) {
+	rows, err := db.QueryContext(ctx, `SELECT `+kindAssignmentColumns+` FROM current_kind_assignment`)
+	if err != nil {
+		return nil, fmt.Errorf("all current assignments: %w", err)
+	}
+	defer rows.Close()
+
+	assignments := []KindAssignment{}
+	for rows.Next() {
+		a, err := scanKindAssignment(rows)
+		if err != nil {
+			return nil, fmt.Errorf("scan kind assignment row: %w", err)
+		}
+		assignments = append(assignments, a)
+	}
+	return assignments, rows.Err()
+}
+
 // AssignmentsForKind returns every historical assignment where the given
 // workout kind was the resolved kind (regardless of source), oldest first --
 // the basis for progression-over-time charts.