Stage 2: Library search, filters and Exercise detail with Flip Animation

- LibraryFilter: word search on names; muscle (primary), equipment and
  level choices that widen within a filter and narrow across filters
- ExerciseBrowser (reusable for the Plan picker) with search field,
  filter sheets showing live result counts, a clear button and an
  empty state
- Exercise detail: start/end Flip Animation at each Mode's pace (still
  with reduced motion), facts, main/secondary muscles, numbered steps

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

lib/src/localization/app_en.arb

@@ -12,18 +12,70 @@
   "plansEmptyBody": "{mode, select, stretching{Put together a stretch routine from the library and it will wait for you here.} other{Put together a workout from the library and it will wait for you here.}}",
   "@plansEmptyBody": {
     "placeholders": {
-      "mode": {"type": "String"}
+      "mode": {
+        "type": "String"
+      }
     }
   },
   "libraryTitle": "Library",
   "librarySubtitle": "{mode, select, stretching{{count, plural, =1{1 stretch} other{{count} stretches}}} other{{count, plural, =1{1 exercise} other{{count} exercises}}}}",
   "@librarySubtitle": {
     "placeholders": {
-      "mode": {"type": "String"},
-      "count": {"type": "int"}
+      "mode": {
+        "type": "String"
+      },
+      "count": {
+        "type": "int"
+      }
     }
   },
   "historyTitle": "History",
   "historyEmptyTitle": "Nothing logged yet",
-  "historyEmptyBody": "Finished sessions show up here with their date and duration."
+  "historyEmptyBody": "Finished sessions show up here with their date and duration.",
+  "librarySubtitleFiltered": "{mode, select, stretching{{shown} of {total} stretches} other{{shown} of {total} exercises}}",
+  "@librarySubtitleFiltered": {
+    "placeholders": {
+      "mode": {
+        "type": "String"
+      },
+      "shown": {
+        "type": "int"
+      },
+      "total": {
+        "type": "int"
+      }
+    }
+  },
+  "searchHint": "{mode, select, stretching{Search stretches} other{Search exercises}}",
+  "@searchHint": {
+    "placeholders": {
+      "mode": {
+        "type": "String"
+      }
+    }
+  },
+  "searchClear": "Clear search",
+  "filterMuscle": "Muscle",
+  "filterEquipment": "Equipment",
+  "filterLevel": "Level",
+  "clearFilters": "Clear filters",
+  "showResults": "{count, plural, =0{No results} =1{Show 1 result} other{Show {count} results}}",
+  "@showResults": {
+    "placeholders": {
+      "count": {
+        "type": "int"
+      }
+    }
+  },
+  "noMatchesTitle": "No matches",
+  "noMatchesBody": "Try fewer words, or clear the filters to see everything again.",
+  "detailMainMuscles": "Main muscles",
+  "detailAlsoWorks": "Also works",
+  "detailHowTo": "How to do it",
+  "detailLevel": "Level",
+  "detailEquipment": "Equipment",
+  "detailType": "Type",
+  "equipmentNone": "None listed",
+  "flipStart": "Start position",
+  "flipEnd": "End position"
 }