Surface routine usage, starter-copy notices, and a grouped exercise picker

Routine detail gains a read-time Usage section (last trained, completed
workout count, linked schedules) resolved through the clone redirect, and
both it and the edit sheet now explain that editing a starter saves your
own copy. The add-exercise picker adopts the same curated category
sections and name/category/muscle search as the exercise library.

Claude-Session: https://claude.ai/code/session_01H8VxUX4ckjU3vRF5M4L5FV

Workouts/Views/Routines/RoutineAddEditView.swift

@@ -77,9 +77,15 @@ struct RoutineAddEditView: View {
     @ViewBuilder
     private func form(for routine: Routine?) -> some View {
         Form {
-            Section(header: Text("Name")) {
+            Section {
                 TextField("Name", text: $name)
                     .bold()
+            } header: {
+                Text("Name")
+            } footer: {
+                if let routineID, SeedLibrary.isSeed(id: routineID) {
+                    Text("Saving changes to a starter routine creates your own copy; the starter stays available in the gallery.")
+                }
             }
 
             Section(header: Text("Appearance")) {