feat: add voice input mic button via Web Speech API

- index.html: add #btnMic (hidden by default, shown if browser supports
  SpeechRecognition) and #micStatus listening indicator inside .composer-box

- boot.js: IIFE-scoped mic handler wired to Web Speech API
  * recognition.continuous=false (auto-stops after ~2s silence)
  * recognition.interimResults=true (live transcript preview in textarea)
  * Toggles .recording class + shows #micStatus while active
  * Handles 'not-allowed', 'no-speech', 'network' errors via showToast()
  * btnSend.onclick stops active recognition before sending
  * Entire feature disabled/hidden gracefully when API unavailable

- style.css: .mic-btn, .mic-btn.recording (red pulse animation),
  .mic-status, .mic-dot, @keyframes mic-pulse

- tests/test_sprint20.py: 46 tests covering HTML structure, CSS rules,
  JS logic, error handling, and regression checks (376 total, all pass)

No API keys, no external libraries, no server changes. Browser-only.
Works in Chrome, Edge, Safari (partial). Firefox unsupported (hides button).

static/index.html

@@ -213,6 +213,7 @@
           Drop files to upload to workspace
         </div>
         <div class="attach-tray" id="attachTray"></div>
+        <div class="mic-status" id="micStatus" style="display:none"><span class="mic-dot"></span> Listening…</div>
         <textarea id="msg" rows="1" placeholder="Message Hermes…"></textarea>
         <div class="composer-footer">
           <div class="composer-left">
@@ -220,6 +221,14 @@
             <button class="icon-btn" id="btnAttach" title="Attach files">
               <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><path d="M21.44 11.05l-9.19 9.19a6 6 0 0 1-8.49-8.49l9.19-9.19a4 4 0 0 1 5.66 5.66l-9.2 9.19a2 2 0 0 1-2.83-2.83l8.49-8.48"/></svg>
             </button>
+            <button class="icon-btn mic-btn" id="btnMic" title="Voice input" style="display:none">
+              <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
+                <rect x="9" y="1" width="6" height="12" rx="3"/>
+                <path d="M5 10a7 7 0 0 0 14 0"/>
+                <line x1="12" y1="19" x2="12" y2="23"/>
+                <line x1="8" y1="23" x2="16" y2="23"/>
+              </svg>
+            </button>
           </div>
           <div class="composer-right">
             <button class="send-btn" id="btnSend">