Add the Library tab: reorderable routines pane and searchable grouped exercises pane

A fourth tab promotes routine and exercise management out of Settings.
LibraryView switches between two segments on one navigation stack. The
routines pane (RoutineListView reborn as RoutinesLibraryView) sorts by
the user's order, gains drag-to-reorder writing only changed orders,
swipe actions for duplicate/edit/delete, a Starter badge on bundled
seeds, and a last-trained caption. The exercises pane groups the library
into curated category sections searchable by name, category, or muscle.

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

Workouts/ContentView.swift

@@ -18,6 +18,9 @@ struct ContentView: View {
             Tab("Progress", systemImage: "chart.line.uptrend.xyaxis") {
                 ProgressTabView()
             }
+            Tab("Library", systemImage: "books.vertical.fill") {
+                LibraryView()
+            }
             Tab("Settings", systemImage: "gearshape.2") {
                 SettingsView()
             }