Add read-aloud: reads story from cursor to end using Web Speech API

- 🔊 button at far-right of toolbar; toggles to ⏹ while reading
- Extracts plain text from cursor position to end of document via
  editor.state.doc.textBetween — works with cursor or selection
- Splits into sentence chunks to work around Chrome's ~15s utterance
  cutoff bug; each chunk's onend fires the next
- isReadingRef guards the closure so Stop cancels mid-sentence cleanly
- Gentle pulse animation on the active button (reading-pulse keyframe)
- No server required — uses built-in browser speechSynthesis

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

frontend/src/components/Toolbar.jsx

@@ -1,7 +1,50 @@
-import { useRef } from 'react'
+import { useRef, useState } from 'react'
 
 export default function Toolbar({ editor, onImageUpload, fontSize, onFontSizeChange }) {
   const fileRef      = useRef()
+  const [isReading, setIsReading] = useState(false)
+  const isReadingRef = useRef(false)   // ref so closure in next() always sees current value
+
+  function startReading() {
+    if (!('speechSynthesis' in window)) return
+
+    // Grab text from cursor (or selection start) to end of document
+    const { from } = editor.state.selection
+    const end  = editor.state.doc.content.size
+    const text = editor.state.doc.textBetween(from, end, '\n', ' ').trim()
+    if (!text) return
+
+    // Split into sentences — Chrome stops an utterance after ~15 s if it's too long
+    const chunks = (
+      text.match(/[^.!?…]+[.!?…]*['"'"]?\s*/g)
+        ?.map(s => s.trim())
+        .filter(Boolean)
+    ) || [text]
+
+    speechSynthesis.cancel()   // clear any leftover utterance
+    isReadingRef.current = true
+    setIsReading(true)
+
+    let idx = 0
+    function next() {
+      if (!isReadingRef.current || idx >= chunks.length) {
+        isReadingRef.current = false
+        setIsReading(false)
+        return
+      }
+      const u = new SpeechSynthesisUtterance(chunks[idx++])
+      u.onend  = next
+      u.onerror = () => { isReadingRef.current = false; setIsReading(false) }
+      speechSynthesis.speak(u)
+    }
+    next()
+  }
+
+  function stopReading() {
+    isReadingRef.current = false
+    setIsReading(false)
+    speechSynthesis.cancel()
+  }
 
   if (!editor) return null
 
@@ -83,6 +126,16 @@ export default function Toolbar({ editor, onImageUpload, fontSize, onFontSizeCha
       <button className="toolbar-btn font-btn" onMouseDown={e => { e.preventDefault(); onFontSizeChange(-1) }} title="Smaller text">A−</button>
       <span className="toolbar-font-size">{fontSize}px</span>
       <button className="toolbar-btn font-btn" onMouseDown={e => { e.preventDefault(); onFontSizeChange(+1) }} title="Larger text">A+</button>
+
+      <span className="toolbar-sep" />
+
+      <button
+        className={`toolbar-btn read-aloud-btn${isReading ? ' reading-active' : ''}`}
+        onMouseDown={e => { e.preventDefault(); isReading ? stopReading() : startReading() }}
+        title={isReading ? 'Stop reading' : 'Read aloud from cursor (reads to end of story)'}
+      >
+        {isReading ? '⏹' : '🔊'}
+      </button>
     </div>
   )
 }

frontend/src/styles/index.css

@@ -1463,6 +1463,21 @@ button { cursor: pointer; font-family: inherit; }
   font-variant-numeric: tabular-nums;
 }
 
+/* ── Read Aloud ───────────────────────────────────────── */
+
+.read-aloud-btn { font-size: 1rem; line-height: 1; padding: 0.2rem 0.45rem; }
+
+.read-aloud-btn.reading-active {
+  color: var(--accent-hi);
+  border-color: var(--accent);
+  animation: reading-pulse 1.8s ease-in-out infinite;
+}
+
+@keyframes reading-pulse {
+  0%, 100% { opacity: 1; }
+  50%       { opacity: 0.45; }
+}
+
 /* ── Writing Prompt ───────────────────────────────────── */
 
 .prompt-wrap { position: relative; }