feat: eliminate URL dualism — computed permalinks, conversations support

- Add computed permalink in data cascade for existing posts without
  frontmatter permalink (converts file path to Indiekit URL)
- Fix ogSlug filter and computed data for new 5-segment URL structure
- Add conversations API as build-time data source
- Merge conversations + webmentions in webmentionsForUrl filter with
  deduplication and legacy /content/ URL alias computation
- Sidebar widget fetches from both webmention-io and conversations APIs
- Update webmention-debug page with conversationMentions parameter

_data/conversationMentions.js

@@ -0,0 +1,14 @@
+import EleventyFetch from "@11ty/eleventy-fetch";
+
+export default async function () {
+  try {
+    const data = await EleventyFetch(
+      "http://127.0.0.1:8080/conversations/api/mentions?per-page=10000",
+      { duration: "15m", type: "json" }
+    );
+    return data.children || [];
+  } catch (e) {
+    console.log(`[conversationMentions] API unavailable: ${e.message}`);
+    return [];
+  }
+}

_data/eleventyComputed.js

@@ -16,18 +16,55 @@ import { fileURLToPath } from "node:url";
 const __dirname = dirname(fileURLToPath(import.meta.url));
 
 export default {
-  ogSlug: (data) => {
-    const url = data.page?.url;
-    if (!url) return "";
-    return url.replace(/\/$/, "").split("/").pop();
-  },
+  eleventyComputed: {
+    // Compute permalink from file path for posts without explicit frontmatter permalink.
+    // Pattern: content/{type}/{yyyy}-{MM}-{dd}-{slug}.md → /{type}/{yyyy}/{MM}/{dd}/{slug}/
+    permalink: (data) => {
+      // If frontmatter already has permalink, use it (new posts from preset)
+      if (data.permalink) return data.permalink;
 
-  hasOgImage: (data) => {
-    const url = data.page?.url;
-    if (!url) return false;
-    const slug = url.replace(/\/$/, "").split("/").pop();
-    if (!slug) return false;
-    const ogPath = resolve(__dirname, "..", ".cache", "og", `${slug}.png`);
-    return existsSync(ogPath);
+      // Only compute for files matching the dated post pattern
+      const inputPath = data.page?.inputPath || "";
+      const match = inputPath.match(
+        /content\/([^/]+)\/(\d{4})-(\d{2})-(\d{2})-(.+)\.md$/
+      );
+      if (match) {
+        const [, type, year, month, day, slug] = match;
+        return `/${type}/${year}/${month}/${day}/${slug}/`;
+      }
+
+      // For non-matching files (pages, root files), preserve existing permalink or let Eleventy decide
+      return data.permalink;
+    },
+
+    // OG image slug — must reconstruct date-prefixed filename from URL segments.
+    // OG images are generated as {yyyy}-{MM}-{dd}-{slug}.png by lib/og.js.
+    // With new URL structure /type/yyyy/MM/dd/slug/, we reconstruct the filename.
+    ogSlug: (data) => {
+      const url = data.page?.url || "";
+      const segments = url.split("/").filter(Boolean);
+      // Date-based URL: /type/yyyy/MM/dd/slug/ → 5 segments
+      if (segments.length === 5) {
+        const [, year, month, day, slug] = segments;
+        return `${year}-${month}-${day}-${slug}`;
+      }
+      // Fallback: last segment (for pages, legacy URLs)
+      return segments[segments.length - 1] || "";
+    },
+
+    hasOgImage: (data) => {
+      const url = data.page?.url || "";
+      const segments = url.split("/").filter(Boolean);
+      let slug;
+      if (segments.length === 5) {
+        const [, year, month, day, s] = segments;
+        slug = `${year}-${month}-${day}-${s}`;
+      } else {
+        slug = segments[segments.length - 1] || "";
+      }
+      if (!slug) return false;
+      const ogPath = resolve(__dirname, "..", ".cache", "og", `${slug}.png`);
+      return existsSync(ogPath);
+    },
   },
 };