Add live reload support for local development

Replace static HTTP server with livereload-based dev server that watches
posts/, layout/, and static/ directories for changes, rebuilds the site,
and auto-refreshes the browser.

devserver.py

@@ -0,0 +1,25 @@
+#!/usr/bin/env python3
+"""Development server with live reload."""
+
+import subprocess
+import sys
+
+from livereload import Server
+
+
+def rebuild(flag):
+    subprocess.run(["uv", "run", "python", "makesite.py", flag])
+
+
+def main():
+    flag = sys.argv[1] if len(sys.argv) > 1 else "--local"
+    rebuild(flag)
+    server = Server()
+    server.watch("posts/**/*.md", lambda: rebuild(flag))
+    server.watch("layout/*.html", lambda: rebuild(flag))
+    server.watch("static/**/*", lambda: rebuild(flag))
+    server.serve(root="_site", port=8000, open_url_delay=1)
+
+
+if __name__ == "__main__":
+    main()