feat(work): auto-tick epic story bullets when a story finishes

- Add tickStoryBulletInEpic(workRoot, epic, story) helper that finds
  the bullet in the parent epic's `## Stories` section linking to the
  given story folder and flips `- [ ]` to `- [x]`. Idempotent.
- applyApprovedState now ticks the parent epic bullet whenever a
  story flips to status: done (alongside the existing per-task tick
  and epic-status flip). Epic file gets staged on either ticked-or-
  flipped, not just flipped.
- Backfill all 3 existing epics: 21 bullets ticked to match their
  already-done story statuses (binder-wrap-helper x3, library-
  evaluation-policy x9, ci-security-and-supply-chain x9).

scripts/work/dispatch.mjs

@@ -191,6 +191,40 @@ export function readFrontmatterStatus(content) {
   return m ? m[1].trim() : null;
 }
 
+/**
+ * Tick the bullet in an epic's `## Stories` section that links to the given
+ * story folder. Idempotent: returns false if the bullet is already ticked or
+ * not present. Mirrors the per-task tick that already happens inside story
+ * files, applied at the parent-epic granularity.
+ */
+export function tickStoryBulletInEpic(workRoot, epicId, storyId) {
+  const epicFile = path.join(workRoot, epicId, "_epic.md");
+  if (!fs.existsSync(epicFile)) return false;
+  const content = fs.readFileSync(epicFile, "utf8");
+  const lines = content.split("\n");
+  let inStories = false;
+  let changed = false;
+  for (let i = 0; i < lines.length; i++) {
+    if (lines[i].startsWith("## ")) {
+      inStories = /^##\s+Stories\b/i.test(lines[i]);
+      continue;
+    }
+    if (!inStories) continue;
+    if (
+      lines[i].includes(`(${storyId}/_story.md)`) ||
+      lines[i].includes(`(./${storyId}/_story.md)`)
+    ) {
+      if (/\[\s\]/.test(lines[i])) {
+        lines[i] = lines[i].replace(/\[\s\]/, "[x]");
+        changed = true;
+      }
+      break;
+    }
+  }
+  if (changed) fs.writeFileSync(epicFile, lines.join("\n"));
+  return changed;
+}
+
 /**
  * If all stories in an epic are `status: done`, flip the epic's own
  * frontmatter to `status: done`. Returns true if it flipped, false otherwise.
@@ -457,12 +491,14 @@ function applyApprovedState(next) {
   fs.writeFileSync(next.storyPath, content);
 
   let epicFlipped = false;
+  let epicBulletTicked = false;
   if (storyFlipped) {
+    epicBulletTicked = tickStoryBulletInEpic(WORK_ROOT, next.epic, next.story);
     epicFlipped = flipEpicDoneIfAllStoriesDone(WORK_ROOT, next.epic);
   }
 
   const filesToStage = [path.relative(REPO_ROOT, next.storyPath)];
-  if (epicFlipped) {
+  if (epicFlipped || epicBulletTicked) {
     filesToStage.push(
       path.relative(REPO_ROOT, path.join(WORK_ROOT, next.epic, "_epic.md")),
     );