fix: add watcher debounce for rapid successive file changes

When Micropub creates a post, the markdown file is written twice in quick
succession — first the initial content, then ~2s later a syndication update
adds syndication URLs. Without debouncing, the watcher rebuilds from the
first write and misses the second, causing "Also on" links to not appear.

- awaitWriteFinish (2s stability threshold): delays watcher events until
  the file hasn't been written to for 2 seconds
- setWatchThrottleWaitTime (3s): groups all file changes within 3 seconds
  into a single build

Confab-Link: http://localhost:8080/sessions/956f4251-b4a9-4bc9-b214-53402ad1fe63

eleventy.config.js

@@ -53,6 +53,20 @@ export default function (eleventyConfig) {
   eleventyConfig.watchIgnores.add(".cache/unfurl");
   eleventyConfig.watchIgnores.add(".cache/unfurl/**");
 
+  // Watcher tuning: handle rapid successive file changes
+  // When a post is created via Micropub, the file is written twice in quick
+  // succession: first the initial content, then ~2s later a Micropub update
+  // adds syndication URLs. awaitWriteFinish delays the watcher event until
+  // the file is stable (no writes for 2s), so both changes are captured in
+  // one build. The throttle adds a 3s build-level debounce on top.
+  eleventyConfig.setChokidarConfig({
+    awaitWriteFinish: {
+      stabilityThreshold: 2000,
+      pollInterval: 100,
+    },
+  });
+  eleventyConfig.setWatchThrottleWaitTime(3000);
+
   // Configure markdown-it with linkify enabled (auto-convert URLs to links)
   const md = markdownIt({
     html: true,