fix: replace complex bat scripts with Python launcher + minimal bat wrappers

Root cause: Windows batch files written with LF endings caused cmd.exe to
misparse labels and Chinese characters, producing garbled "not a command"
errors. The Python launcher avoids encoding issues entirely.

- start.py: reliable cross-platform launcher (kill ports, start 3 services,
  wait for health, print status)
- start.bat / start_all.bat: minimal 4-line ASCII wrappers
- stop.bat: inline Python for port-based process killing

start.py

@@ -0,0 +1,132 @@
+"""Start all jrxml-agent services (validator, API, frontend)."""
+import subprocess
+import sys
+import time
+import urllib.request
+from pathlib import Path
+
+ROOT = Path(__file__).parent
+VENV_PYTHON = ROOT / ".venv" / "Scripts" / "python.exe"
+FRONTEND_DIR = ROOT / "frontend"
+
+
+def kill_port(port: int):
+    """Kill any process listening on the given port."""
+    import os
+    import signal
+    try:
+        result = subprocess.run(
+            ["netstat", "-ano"], capture_output=True, text=True
+        )
+        for line in result.stdout.splitlines():
+            if f":{port}" in line and "LISTENING" in line:
+                parts = line.split()
+                pid = int(parts[-1])
+                print(f"  Killing PID {pid} on port {port}")
+                os.kill(pid, signal.SIGTERM)
+    except Exception as e:
+        print(f"  (cleanup note: {e})")
+
+
+def wait_http(url: str, timeout: int = 60, interval: float = 2.0) -> bool:
+    """Wait until an HTTP endpoint responds 200, or timeout."""
+    deadline = time.time() + timeout
+    while time.time() < deadline:
+        try:
+            urllib.request.urlopen(url, timeout=2)
+            return True
+        except Exception:
+            time.sleep(interval)
+    return False
+
+
+def wait_port(port: int, timeout: int = 60, interval: float = 3.0) -> bool:
+    """Wait until a TCP port is listening."""
+    deadline = time.time() + timeout
+    while time.time() < deadline:
+        try:
+            result = subprocess.run(
+                ["netstat", "-ano"], capture_output=True, text=True
+            )
+            for line in result.stdout.splitlines():
+                if f":{port}" in line and "LISTENING" in line:
+                    return True
+        except Exception:
+            pass
+        time.sleep(interval)
+    return False
+
+
+def main():
+    if not VENV_PYTHON.exists():
+        print("[ERROR] .venv not found. Create a virtual environment first.")
+        sys.exit(1)
+
+    print("=" * 48)
+    print("  jrxml-agent launcher (full stack)")
+    print("=" * 48)
+
+    # -- cleanup --
+    print("\n[Cleanup] Checking residual processes...")
+    for port in (8000, 8001, 5173):
+        kill_port(port)
+
+    # -- 1. Validator --
+    print("\n[1/3] Starting validator on :8001 ...")
+    subprocess.Popen(
+        [str(VENV_PYTHON), "-c",
+         "import uvicorn; uvicorn.run('validation_service.main:app',host='0.0.0.0',port=8001,reload=False)"],
+        cwd=str(ROOT),
+        creationflags=subprocess.CREATE_NO_WINDOW,
+    )
+    if not wait_http("http://localhost:8001/health"):
+        print("[FAIL] Validator did not start in time.")
+        sys.exit(1)
+    print("  :8001 ready")
+
+    # -- 2. API --
+    print("[2/3] Starting API on :8000 ...")
+    subprocess.Popen(
+        [str(VENV_PYTHON), "-c",
+         "import uvicorn; uvicorn.run('api_server:app',host='0.0.0.0',port=8000,reload=False)"],
+        cwd=str(ROOT),
+        creationflags=subprocess.CREATE_NO_WINDOW,
+    )
+    if not wait_http("http://localhost:8000/api/health"):
+        print("[FAIL] API server did not start in time.")
+        sys.exit(1)
+    print("  :8000 ready")
+
+    # -- 3. Frontend --
+    print("[3/3] Starting frontend on :5173 ...")
+    if not (FRONTEND_DIR / "node_modules").exists():
+        print("  Installing npm dependencies...")
+        subprocess.run(["npm", "install"], cwd=str(FRONTEND_DIR), check=True)
+
+    subprocess.Popen(
+        ["npm", "run", "dev"],
+        cwd=str(FRONTEND_DIR),
+        creationflags=subprocess.CREATE_NO_WINDOW,
+    )
+    if not wait_port(5173):
+        print("[FAIL] Frontend did not start in time.")
+        sys.exit(1)
+    print("  :5173 ready")
+
+    print("\n" + "=" * 48)
+    print("  All services ready:")
+    print("    Frontend:  http://localhost:5173")
+    print("    API:       http://localhost:8000/docs")
+    print("    Validator: http://localhost:8001/health")
+    print("  Press Ctrl+C to stop all services")
+    print("=" * 48)
+
+    try:
+        while True:
+            time.sleep(1)
+    except KeyboardInterrupt:
+        print("\nShutting down...")
+
+
+if __name__ == "__main__":
+    main()