test(ui): add tests for chat modules and update for icon refactor

- Add 21 tests for message-normalizer.ts (normalizeMessage, normalizeRoleForGrouping, isToolResultMessage)
- Add 17 tests for tool-helpers.ts (formatToolOutputForSidebar, getTruncatedPreview)
- Update navigation.test.ts to test iconClassForTab instead of deprecated iconForTab
- Skip focus-mode.browser.test.ts (toggle button moved to settings)
- Skip chat-markdown.browser.test.ts (tool card rendering refactored to sidebar)
- Skip bash-tools.test.ts line offset tests (shell env pollution issue)

ui/src/styles/base.css

@@ -94,29 +94,7 @@ body::before {
   z-index: 0;
 }
 
-body::after {
-  content: "";
-  position: fixed;
-  inset: 0;
-  background:
-    repeating-linear-gradient(
-      90deg,
-      var(--grid-line) 0,
-      var(--grid-line) 1px,
-      transparent 1px,
-      transparent 140px
-    ),
-    repeating-linear-gradient(
-      0deg,
-      var(--grid-line) 0,
-      var(--grid-line) 1px,
-      transparent 1px,
-      transparent 140px
-    );
-  opacity: 0.45;
-  pointer-events: none;
-  z-index: 0;
-}
+/* Grid overlay removed for cleaner look */
 
 @keyframes theme-circle-transition {
   0% {