fix(inventory): address code review findings

- Replace setTimeout race in use-item flow with explicit Back button
- Fix collector end handler to re-render current view instead of blanking
- Add appendUseBackButton helper to attach navigation to use results
- Remove unused isInventoryInteraction import
- Fix rarity test type assertions

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

shared/lib/rarity.test.ts

@@ -16,12 +16,12 @@ describe("getRarityConfig", () => {
 
   it("falls back to Common for unknown rarity", () => {
     const result = getRarityConfig("LEGENDARY");
-    expect(result).toEqual(RARITY_CONFIG["C"]);
+    expect(result).toEqual(RARITY_CONFIG["C"]!);
   });
 
   it("falls back to Common for null/undefined input", () => {
-    expect(getRarityConfig(null as any)).toEqual(RARITY_CONFIG["C"]);
-    expect(getRarityConfig(undefined as any)).toEqual(RARITY_CONFIG["C"]);
+    expect(getRarityConfig(null as any)).toEqual(RARITY_CONFIG["C"]!);
+    expect(getRarityConfig(undefined as any)).toEqual(RARITY_CONFIG["C"]!);
   });
 });