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/app.js

@@ -1564,6 +1564,8 @@ function initializeEventListeners() {
       saveToggleState(st);
       agentBtn.classList.toggle('active', mode === 'agent');
       chatBtn.classList.toggle('active', mode === 'chat');
+      agentBtn.setAttribute('aria-pressed', String(mode === 'agent'));
+      chatBtn.setAttribute('aria-pressed', String(mode === 'chat'));
       // Slide the pill to the active button
       const toggle = agentBtn.closest('.mode-toggle');
       if (toggle) toggle.classList.toggle('mode-chat', mode === 'chat');
@@ -1621,11 +1623,13 @@ function initializeEventListeners() {
     const chk = el(checkboxId);
     if (chk) chk.checked = saved;
     btn.classList.toggle('active', saved);
+    btn.setAttribute('aria-pressed', String(saved));
     btn.addEventListener('click', () => {
       const curMode = (loadToggleState().mode) || 'chat';
       const chk = el(checkboxId);
       chk.checked = !chk.checked;
       btn.classList.toggle('active', chk.checked);
+      btn.setAttribute('aria-pressed', String(chk.checked));
       saveToolPref(stateKey, curMode, chk.checked);
       showToolToggleToast(stateKey, chk.checked);
       if (chk.checked) _showToolSplash(stateKey);