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-flash.css

@@ -1,14 +1,12 @@
 @layer components {
+  /* Flash notices — success/warning/error/info feedback banners with auto-dismiss timer. */
 .notice {
     --app-notice-border-color: var(--app-muted-border-color);
     --app-notice-background-color: var(--app-card-background-color);
     --app-notice-accent-color: var(--app-color);
-    /* border: var(--app-border-width) solid var(--app-notice-border-color); */
-    /* border-radius: var(--app-border-radius); */
     background: var(--app-notice-background-color);
     padding: calc(var(--app-spacing) * .5) calc(var(--app-spacing) * 1);
     padding-right: calc(var(--app-spacing) * .5);
-    /* margin-bottom: var(--app-spacing); */
     display: flex;
     align-items: center;
     justify-content: space-between;
@@ -113,10 +111,6 @@
     margin: 0;
 }
 
-/* .flash-stack:has(.notice) {
-    margin-top: var(--app-spacing);
-} */
-
 .app-main-content .flash-stack {
     margin-bottom: var(--app-spacing);
 }