feat(01-04): add TanStack Virtual list virtualization and keyboard navigation hook

- Install @tanstack/react-virtual for virtualized list rendering
- Create useRovingTabIndex hook in src/renderer/lib/keyboard.ts for arrow-key navigation
- Add virtualization to 6 lists: TaskQueue, ApprovalList, ActivityList, CostList, AgentRoster, MessageList
- MessageList uses measureElement for variable-height message items with auto-scroll
- All 6 lists have role="listbox" with role="option" on rows for accessibility
- All 6 lists support ArrowDown/ArrowUp/j/k/Home/End keyboard navigation
- Add 8 unit tests for useRovingTabIndex covering all key bindings and edge cases

pnpm-lock.yaml

@@ -26,6 +26,9 @@ importers:
       '@phosphor-icons/react':
         specifier: 2.1.10
         version: 2.1.10(react-dom@19.2.4(react@19.2.4))(react@19.2.4)
+      '@tanstack/react-virtual':
+        specifier: ^3.13.23
+        version: 3.13.23(react-dom@19.2.4(react@19.2.4))(react@19.2.4)
       clsx:
         specifier: 2.1.1
         version: 2.1.1
@@ -1012,6 +1015,15 @@ packages:
     peerDependencies:
       vite: ^5.2.0 || ^6 || ^7
 
+  '@tanstack/react-virtual@3.13.23':
+    resolution: {integrity: sha512-XnMRnHQ23piOVj2bzJqHrRrLg4r+F86fuBcwteKfbIjJrtGxb4z7tIvPVAe4B+4UVwo9G4Giuz5fmapcrnZ0OQ==}
+    peerDependencies:
+      react: ^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0
+      react-dom: ^16.8.0 || ^17.0.0 || ^18.0.0 || ^19.0.0
+
+  '@tanstack/virtual-core@3.13.23':
+    resolution: {integrity: sha512-zSz2Z2HNyLjCplANTDyl3BcdQJc2k1+yyFoKhNRmCr7V7dY8o8q5m8uFTI1/Pg1kL+Hgrz6u3Xo6eFUB7l66cg==}
+
   '@types/babel__core@7.20.5':
     resolution: {integrity: sha512-qoQprZvz5wQFJwMDqeseRXWv3rqMvhgpbXFfVyWhbx9X47POIA6i/+dXefEmZKoAgOaTdaIgNSMqMIU61yRyzA==}
 
@@ -3624,6 +3636,14 @@ snapshots:
       tailwindcss: 4.2.1
       vite: 7.3.1(@types/node@25.5.0)(jiti@2.6.1)(lightningcss@1.31.1)
 
+  '@tanstack/react-virtual@3.13.23(react-dom@19.2.4(react@19.2.4))(react@19.2.4)':
+    dependencies:
+      '@tanstack/virtual-core': 3.13.23
+      react: 19.2.4
+      react-dom: 19.2.4(react@19.2.4)
+
+  '@tanstack/virtual-core@3.13.23': {}
+
   '@types/babel__core@7.20.5':
     dependencies:
       '@babel/parser': 7.29.0