Fix docs build race condition by using build:self

The docs build scripts were running 'pnpm run --filter @fedify/* -r build',
which caused each package's build script to recursively build its dependencies
via 'pnpm --filter @fedify/xxx... run build:self'. When multiple packages ran
in parallel, they would try to build shared dependencies concurrently, causing
race conditions on dist/ directories.

Changed to 'pnpm run --filter @fedify/* -r build:self' so pnpm manages the
dependency order and builds each package exactly once.

Co-Authored-By: Claude <[email protected]>

Author: dahlia

docs/package.json

@@ -63,8 +63,8 @@
     "x-forwarded-fetch": "^0.2.0"
   },
   "scripts": {
-    "dev": "cd ../ && pnpm run --filter '@fedify/*' -r build && cd docs/ && vitepress dev --host",
-    "build": "cd ../ && pnpm run --filter '@fedify/*' -r build && cd docs/ && NODE_OPTIONS='--max-old-space-size=8192' vitepress build",
-    "preview": "cd ../ && pnpm run --filter '@fedify/*' -r build && cd docs/ && vitepress preview"
+    "dev": "cd ../ && pnpm run --filter '@fedify/*' -r build:self && cd docs/ && vitepress dev --host",
+    "build": "cd ../ && pnpm run --filter '@fedify/*' -r build:self && cd docs/ && NODE_OPTIONS='--max-old-space-size=8192' vitepress build",
+    "preview": "cd ../ && pnpm run --filter '@fedify/*' -r build:self && cd docs/ && vitepress preview"
   }
 }