Add SPA static file serving from backend

Backend (Server.hs):
- serveStaticOrSpa: serves static files from --static-dir
- SPA fallback: extensionless paths serve index.html
- MIME type mapping for html/css/js/png/svg/ico/woff2

Frontend:
- ES module imports with import map for Mithril CDN
- Build script: tsc + copy index.html + static assets

CLI:
- --static-dir flag (default: frontend/dist)
- scripts/run passes through extra args
- Dockerfile CMD points at /usr/local/share/sis/static

scripts/run

@@ -1,19 +1,21 @@
 #!/usr/bin/env bash
 # Run the sis-server in Docker.
 #
-# Usage: ./scripts/run [--port PORT]
+# Usage: ./scripts/run [--port PORT] [--static-dir DIR] [-- ... extra server args]
 #
 # The server listens on port 8080 inside the container, mapped to PORT
-# on the host (default 8080).  Pass --port to change the host-side port.
+# on the host (default 8080).
 #
 # Examples:
 #   ./scripts/run
 #   ./scripts/run --port 9090
+#   ./scripts/run --static-dir frontend/dist
 set -euo pipefail
 
 PROJECT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
 
 HOST_PORT=8080
+SERVER_ARGS=()
 while [ $# -gt 0 ]; do
     case "$1" in
         --port)
@@ -21,8 +23,8 @@ while [ $# -gt 0 ]; do
             shift 2
             ;;
         *)
-            echo "Unknown option: $1" >&2
-            exit 1
+            SERVER_ARGS+=("$1")
+            shift
             ;;
     esac
 done
@@ -40,4 +42,4 @@ exec docker run --rm -i $([ -t 0 ] && printf -- -t) \
     -w /work \
     -p "${HOST_PORT}:8080" \
     "${IMAGE}" \
-    stack exec sis-server -- --port 8080
+    stack exec sis-server -- --port 8080 "${SERVER_ARGS[@]}"