Accessibility: add labels and toggle states

* Accessibility: ARIA labels and toggle states

Screen readers couldn't name several icon-only controls or tell whether the
tool toggles were on. This adds accessible names and exposes toggle state,
with no behavior or layout change.

- Icon-only buttons get aria-label: web/shell tool toggles, the "more tools"
  overflow button (+ aria-haspopup), and the color-reset buttons.
- Unlabeled inputs/selects get aria-label: memory + skills search, model-picker
  search, memory sort, theme font/density selects, and the new-memory / skill
  (title, when-to-use, how, tags) fields, which only had a visual floating label.
- Toggle state via aria-pressed, kept in sync at the existing .active write
  sites: web/shell toggles (setupToggle) and the Agent/Chat mode buttons
  (initModeToggle). Static aria-pressed added in the markup so the attribute
  exists before JS runs.

Scope: first slice of the ROADMAP accessibility pass. Focus-visible/contrast,
reduced-motion, and modal dialog roles/focus-trap are left for follow-ups.

Checks: node --check static/app.js. No Python touched.

* Accessibility: mark chat log busy while streaming

The chat log is an aria-live="polite" region, so streaming a response
token-by-token made screen readers announce every partial update — noisy and
unreadable. Set aria-busy="true" on #chat-history while a response streams and
back to "false" in the stream's finally block. Assistive tech then waits for
the settled message and announces it once.

Checks: node --check static/js/chat.js.

static/js/chat.js

@@ -964,6 +964,11 @@ import createResearchSynapse from './researchSynapse.js';
         return;
       }
 
+      // Mark the chat log busy while streaming so screen readers wait for the
+      // settled response instead of announcing every token. Cleared in finally.
+      const _chatLog = document.getElementById('chat-history');
+      if (_chatLog) _chatLog.setAttribute('aria-busy', 'true');
+
       const reader = res.body.getReader();
       const decoder = new TextDecoder();
       let buffer = '';
@@ -2702,6 +2707,9 @@ import createResearchSynapse from './researchSynapse.js';
       }
     } finally {
       clearProcessingProbe();
+      // Streaming done — let screen readers announce the settled response.
+      const _chatLogDone = document.getElementById('chat-history');
+      if (_chatLogDone) _chatLogDone.setAttribute('aria-busy', 'false');
       // Always clean up research tracking regardless of background state
       _researchingStreamIds.delete(streamSessionId);
       if (_researchingStreamIds.size === 0) {