feat(build): sync vendored directories from GitHub on start and build

Adds sync-directories.js script that fetches 5chan-directories.json from bitsocialhq/lists and updates the vendored fallback. Runs before generate:assets in prestart and prebuild to ensure the fallback is fresh for every build. Non-fatal: if fetch fails, existing file is kept.

scripts/sync-directories.js

@@ -0,0 +1,57 @@
+// Best-effort sync of 5chan-directories.json from GitHub
+// Updates the vendored fallback in src/data/ so production builds ship a fresh snapshot.
+// Never fails the build — if the fetch fails (offline, rate-limited, etc.), the existing file is kept.
+
+import { writeFileSync, readFileSync } from 'fs';
+import { join, dirname } from 'path';
+import { fileURLToPath } from 'url';
+
+const __filename = fileURLToPath(import.meta.url);
+const __dirname = dirname(__filename);
+
+const GITHUB_URL = 'https://raw.githubusercontent.com/bitsocialhq/lists/master/5chan-directories.json';
+const OUTPUT_PATH = join(__dirname, '..', 'src', 'data', '5chan-directories.json');
+const TIMEOUT_MS = 5000;
+
+const sync = async () => {
+  try {
+    const controller = new AbortController();
+    const timeout = setTimeout(() => controller.abort(), TIMEOUT_MS);
+
+    const response = await fetch(GITHUB_URL, { signal: controller.signal });
+    clearTimeout(timeout);
+
+    if (!response.ok) {
+      throw new Error(`HTTP ${response.status}`);
+    }
+
+    const data = await response.json();
+
+    // Basic sanity check — must have a communities array
+    if (!Array.isArray(data?.communities) || data.communities.length === 0) {
+      throw new Error('Invalid data: missing or empty communities array');
+    }
+
+    const formatted = JSON.stringify(data, null, 2) + '\n';
+
+    // Only write if content actually changed
+    let existing = '';
+    try {
+      existing = readFileSync(OUTPUT_PATH, 'utf8');
+    } catch {
+      // file doesn't exist yet
+    }
+
+    if (formatted === existing) {
+      console.log('✅ Vendored directories already up to date');
+      return;
+    }
+
+    writeFileSync(OUTPUT_PATH, formatted, 'utf8');
+    console.log(`✅ Synced vendored directories (${data.communities.length} communities)`);
+  } catch (e) {
+    console.warn(`⚠️  Could not sync directories from GitHub (keeping existing file): ${e.message}`);
+  }
+};
+
+sync();