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.

Makefile

@@ -3,14 +3,14 @@
 # declare phony targets
 .PHONY: build test typecheck
 
-# run locally (uses --local-stacosys if stacosys is running on port 8100)
+# run locally with live reload (uses --local-stacosys if stacosys is running on port 8100)
+# watches posts/ for changes, regenerates site, and auto-refreshes browser
 site:
 	@if curl -s --connect-timeout 1 http://127.0.0.1:8100/api > /dev/null 2>&1; then \
-		uv run python makesite.py --local-stacosys; \
+		uv run python devserver.py --local-stacosys; \
 	else \
-		uv run python makesite.py --local; \
+		uv run python devserver.py --local; \
 	fi
-	cd _site && python -m SimpleHTTPServer 2> /dev/null || python3 -m http.server
 
 # run type checks
 typecheck:

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()

pyproject.toml

@@ -17,6 +17,7 @@ dependencies = [
 [dependency-groups]
 dev = [
     "black>=24.10.0",
+    "livereload>=2.7.1",
     "mypy>=1.19.1",
     "types-pygments>=2.19.0.20251121",
     "types-requests>=2.32.4.20260107",