fix: replace http.server with SPA fallback server for Vue Router

Python's http.server returns 404 for any path that isn't a real file,
breaking Vue Router history-mode navigation (/campaigns, /queue, etc.).

scripts/spa_server.py: minimal static server that falls back to index.html
for any path that doesn't resolve to a real file in the dist directory.
Both _start_web and the `serve` subcommand now use it.

manage.sh

@@ -85,7 +85,7 @@ _start_web() {
     if [[ -f "frontend/dist/index.html" ]]; then
         info "Starting web on :${WEB_PORT} (static dist — production mode)..."
         conda run --no-capture-output -n "$CONDA_ENV" \
-            python -m http.server "$WEB_PORT" --directory frontend/dist >> "$LOG_WEB" 2>&1 &
+            python scripts/spa_server.py --port "$WEB_PORT" --directory frontend/dist >> "$LOG_WEB" 2>&1 &
     else
         info "Starting web on :${WEB_PORT} (Vite dev server — no dist found)..."
         cd frontend
@@ -264,9 +264,9 @@ case "$cmd" in
   serve)
     # Serve the pre-built frontend dist at port WEB_PORT using a simple static file server.
     # In production, Caddy proxies menagerie.circuitforge.tech/magpie* → this port.
-    info "Serving pre-built frontend on :${WEB_PORT} ..."
+    info "Serving pre-built frontend on :${WEB_PORT} (SPA fallback enabled)..."
     conda run --no-capture-output -n "$CONDA_ENV" \
-        python -m http.server "$WEB_PORT" --directory frontend/dist >> "$LOG_WEB" 2>&1 &
+        python scripts/spa_server.py --port "$WEB_PORT" --directory frontend/dist >> "$LOG_WEB" 2>&1 &
     echo $! > "$PID_WEB"
     ok "Static server up → http://localhost:${WEB_PORT}"
     ;;

scripts/spa_server.py

@@ -0,0 +1,46 @@
+#!/usr/bin/env python3
+"""
+Static SPA server with index.html fallback.
+
+Python's built-in http.server returns 404 for any path that isn't a real
+file, which breaks Vue Router's history-mode navigation. This server falls
+back to index.html for any path that doesn't match a real file, letting the
+client-side router handle the route.
+
+Usage:
+    python scripts/spa_server.py --port 8531 --directory frontend/dist
+"""
+import argparse
+import os
+from http.server import HTTPServer, SimpleHTTPRequestHandler
+
+
+class SPAHandler(SimpleHTTPRequestHandler):
+    def do_GET(self):
+        # Resolve the path to an actual filesystem path inside self.directory.
+        full = self.translate_path(self.path)
+        # If the path doesn't resolve to a real file, serve index.html instead.
+        if not os.path.isfile(full):
+            self.path = "/index.html"
+        super().do_GET()
+
+    def log_message(self, fmt, *args):
+        # Suppress per-request noise; errors still surface.
+        if int(args[1]) >= 400:
+            super().log_message(fmt, *args)
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument("--port", type=int, default=8531)
+    parser.add_argument("--directory", default="frontend/dist")
+    args = parser.parse_args()
+
+    os.chdir(args.directory)
+    server = HTTPServer(("", args.port), SPAHandler)
+    print(f"Serving {args.directory} on :{args.port} (SPA fallback enabled)")
+    server.serve_forever()
+
+
+if __name__ == "__main__":
+    main()