feat(statusbar): word count + reading time + Flesch-Kincaid grade

- src/utils/writing-stats.js — pure module: stripMarkdown() drops fenced
  code blocks, inline code, image URLs, link URLs, headings, blockquote
  markers, list bullets, and emphasis markers so the word count reflects
  the prose a reader actually consumes (the convention used by Hemingway,
  iA Writer). splitSentences / countSyllables use Flesch's standard
  heuristics. computeStats returns wordCount, sentenceCount,
  syllableCount, readingTimeMinutes (default 220 wpm),
  fleschKincaidGrade, charCount.
- src/renderer.js — _updateStatusBar now calls computeStats and updates
  three new status items: ~X min read, Grade N.N, and the existing Words
  + Chars counters use the stripped count.
- src/index.html — two new status items: #reading-time and #grade-level.

Tests (23 new, tests/writing-stats.test.js): markdown stripping (fenced,
inline, images, links, wikilinks, headings, lists, emphasis, HTML),
sentence splitter edge cases, syllable heuristic (short words, silent e,
empty), and computeStats with custom wpm + null-safe inputs.

Full suite: 68 suites, 789 tests, lint+format clean.

Amit Haridas

src/utils/writing-stats.js

@@ -0,0 +1,147 @@
+/**
+ * Writing stats — word count, reading time, Flesch-Kincaid grade level.
+ *
+ * Pure, dependency-free module. The renderer pulls this into a status-bar
+ * widget that updates on every keystroke. Counts exclude code fences and
+ * link/image URLs (the prose a reader actually consumes), which is what
+ * serious writing tools (Hemingway, iA Writer) do.
+ *
+ * Flesch-Kincaid grade level is the standard US-grade readability score:
+  grade = 0.39 * (words/sentences) + 11.8 * (syllables/words) - 15.59
+ * Used widely in education and journalism to gauge reading difficulty.
+ *
+ * @module writing-stats
+ */
+
+/**
+ * Strip markdown chrome so we count the prose a reader actually sees.
+ *  - fenced code blocks ```…```
+ *  - inline code `…`
+ *  - image markup ![alt](url)
+ *  - link markup [text](url) → keep "text" only
+ *  - emphasis markers *, _, **, __
+ *  - heading hashes at line start
+ *  - blockquote markers
+ *  - list bullets at line start (- * +)
+ *  - HTML comments <!-- … -->
+ */
+function stripMarkdown(content) {
+  if (typeof content !== 'string') return '';
+  let s = content;
+  // Fenced code blocks: drop the whole block including the fences
+  s = s.replace(/```[\s\S]*?```/g, ' ');
+  s = s.replace(/~~~[\s\S]*?~~~/g, ' ');
+  // Inline code
+  s = s.replace(/`[^`\n]*`/g, ' ');
+  // Images: drop entirely (the URL is not prose)
+  s = s.replace(/!\[[^\]]*\]\([^)]*\)/g, ' ');
+  // Links: keep the text, drop the URL part
+  s = s.replace(/\[([^\]]*)\]\([^)]*\)/g, '$1');
+  // Wikilinks: keep the visible label
+  s = s.replace(/\[\[([^\]|]+)(\|([^\]]+))?\]\]/g, (_, a, _b, c) => (c || a));
+  // Headings at line start
+  s = s.replace(/^\s{0,3}#{1,6}\s+/gm, '');
+  // Blockquote markers
+  s = s.replace(/^\s{0,3}>\s?/gm, '');
+  // List bullets / numbers at line start
+  s = s.replace(/^\s{0,3}([-*+]|\d+\.)\s+/gm, '');
+  // Emphasis markers
+  s = s.replace(/(\*\*|__)(.*?)\1/g, '$2');
+  s = s.replace(/(\*|_)(.*?)\1/g, '$2');
+  // Strikethrough
+  s = s.replace(/~~(.*?)~~/g, '$1');
+  // HTML comments
+  s = s.replace(/<!--[\s\S]*?-->/g, ' ');
+  // Horizontal rules
+  s = s.replace(/^\s*([-*_])\s*\1\s*\1[\s\S]*?$/gm, ' ');
+  return s;
+}
+
+/** Split prose into sentences. Robust enough for ASCII prose + common punctuation. */
+function splitSentences(prose) {
+  if (!prose) return [];
+  // Split on . ! ? followed by whitespace or end. Keep abbreviations rough.
+  const parts = prose.split(/(?<=[.!?])\s+/);
+  return parts
+    .map((s) => s.trim())
+    .filter((s) => /[A-Za-z0-9À-ɏ]/.test(s) && s.length >= 2);
+}
+
+/**
+ * Approximate syllable count for an English word. The standard regex-based
+ * heuristic (Flesch's original) — accurate to within ±1 syllable for ~80%
+ * of common English words, which is good enough for grade-level scoring.
+ */
+function countSyllablesInWord(word) {
+  if (!word) return 0;
+  const w = word.toLowerCase().replace(/[^a-z]/g, '');
+  if (w.length === 0) return 0;
+  if (w.length <= 3) return 1;
+  // Drop trailing silent e, es, ed
+  let stripped = w.replace(/(?:[^laeiouy]es|ed|[^laeiouy]e)$/, '');
+  stripped = stripped.replace(/^y/, '');
+  const matches = stripped.match(/[aeiouy]{1,2}/g);
+  return matches ? matches.length : 1;
+}
+
+function countSyllables(prose) {
+  const words = (prose.match(/\b[A-Za-z'À-ɏ]+\b/g) || []);
+  let total = 0;
+  for (const w of words) total += countSyllablesInWord(w);
+  return total;
+}
+
+function countWords(prose) {
+  if (!prose) return 0;
+  const matches = prose.match(/\b[\w'À-ɏ]+\b/g);
+  return matches ? matches.length : 0;
+}
+
+/**
+ * Compute the full writing-stats report for a markdown document.
+ *
+ * @param {string} content raw markdown
+ * @param {object} [opts]
+ * @param {number} [opts.wordsPerMinute=220] average reading speed for English prose
+ * @returns {{
+ *   wordCount:number,
+ *   sentenceCount:number,
+ *   syllableCount:number,
+ *   readingTimeMinutes:number,
+ *   fleschKincaidGrade:number|null,
+ *   charCount:number
+ * }}
+ */
+function computeStats(content, opts = {}) {
+  const prose = stripMarkdown(content);
+  const words = countWords(prose);
+  const sentences = splitSentences(prose).length;
+  const syllables = countSyllables(prose);
+  const wpm = typeof opts.wordsPerMinute === 'number' && opts.wordsPerMinute > 0 ? opts.wordsPerMinute : 220;
+  const readingTimeMinutes = words > 0 ? words / wpm : 0;
+
+  let grade = null;
+  if (sentences > 0 && words > 0) {
+    grade = 0.39 * (words / sentences) + 11.8 * (syllables / words) - 15.59;
+    // Round to one decimal for status-bar display; round-trips cleanly.
+    grade = Math.round(grade * 10) / 10;
+  }
+
+  return {
+    wordCount: words,
+    sentenceCount: sentences,
+    syllableCount: syllables,
+    readingTimeMinutes,
+    fleschKincaidGrade: grade,
+    charCount: prose.replace(/\s/g, '').length,
+  };
+}
+
+module.exports = {
+  stripMarkdown,
+  splitSentences,
+  countSyllablesInWord,
+  countSyllables,
+  countWords,
+  computeStats,
+};