fix: web/ quick wins — CSS cleanup, ARIA tabs, and file header comments

CSS:
- Remove duplicate li::before block in app-search.css
- Fix typo: search-reuslt → search-result in app-search.css
- Remove commented-out CSS rules in app-flash.css
- Add descriptive header comment to all 27 CSS component files

JS:
- Complete WAI-ARIA Tabs pattern: generate IDs, add aria-controls on
  tab buttons and aria-labelledby on tab panels (app-tabs.js)
- Add JSDoc header comments to ~33 JS files (core + components)
- Add explanatory block comment to app-boot.js (why classic IIFE)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

web/css/components/app-search.css

@@ -1,4 +1,5 @@
 @layer components {
+  /* Global sidebar search — input, result list, preview rows, and search result cards. */
 .app-search {
     position: relative;
     padding: 0 var(--app-spacing);
@@ -83,18 +84,6 @@ ul.app-search-preview {
 .search-details-hidden ul.app-search-preview {
   display: none;
 }
-ul.app-search-preview li::before {
-    content: "";
-    position: absolute;
-    left: 17px;
-    bottom: 11px;
-    width: 8px;
-    height: 10px;
-    background: transparent;
-    border-left: 1px solid var(--app-border);
-    border-bottom: 1px solid var(--app-border);
-    border-bottom-left-radius: 6px;
-}
 
 ul.app-search-preview li {
   position: relative;
@@ -146,7 +135,7 @@ ul.app-search-preview:has(li) {
     align-items: flex-start;
 }
 
-.search-reuslt-title-container {
+.search-result-title-container {
     display: flex;
     align-items: center;
     gap: 10px;