feat: Tauri desktop shell — Rust backend + config files + build scripts

- desktop/Cargo.toml: Tauri + plugins (dialog, notification, fs, updater)
- desktop/tauri.conf.json: Windows (.msi/.nsis) + Linux (.deb/.AppImage) config
- desktop/src/main.rs: spawn Python backend, health check, tray icon, commands
- desktop/build.rs: Tauri build hook
- desktop/python-embed/sidecar.py: uvicorn launcher with port auto-detect
- build-windows.bat: automated Windows build with Python embed download
- build-linux.sh: automated Linux build with venv
- desktop/README.md: architecture doc + usage guide
- desktop/validate-structure.sh: CI validation script
- ROADMAP.md: #77 Tauri Desktop section added

desktop/python-embed/sidecar.py

@@ -0,0 +1,72 @@
+#!/usr/bin/env python3
+"""
+ObsiGate Desktop — Sidecar Launcher
+====================================
+Lancé par le shell Tauri, démarre le backend FastAPI.
+Utilise le port 17890 (127.0.0.1 uniquement, pas d'exposition réseau).
+"""
+import sys
+import os
+import subprocess
+import time
+import signal
+
+BACKEND_DIR = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
+HOST = "127.0.0.1"
+PORT = int(os.environ.get("OBSIGATE_PORT", "17890"))
+
+
+def find_free_port(start: int) -> int:
+    """Trouve le premier port libre à partir de `start`."""
+    import socket
+    port = start
+    while port < start + 100:
+        with socket.socket(socket.AF_INET, socket.SOCK_STREAM) as s:
+            if s.connect_ex((HOST, port)) != 0:
+                return port
+        port += 1
+    raise RuntimeError(f"No free port found in range {start}-{start+99}")
+
+
+def main():
+    port = find_free_port(PORT)
+
+    # Create log directory
+    if sys.platform == "win32":
+        log_dir = os.path.join(os.environ.get("APPDATA", os.path.expanduser("~")), "ObsiGate", "logs")
+    else:
+        log_dir = os.path.join(os.path.expanduser("~"), ".local", "share", "obsigate", "logs")
+    os.makedirs(log_dir, exist_ok=True)
+
+    log_file = os.path.join(log_dir, "backend.log")
+    print(f"ObsiGate backend starting on {HOST}:{port} — logs: {log_file}")
+
+    # Launch uvicorn
+    cmd = [
+        sys.executable,
+        "-m", "uvicorn",
+        "backend.main:app",
+        "--host", HOST,
+        "--port", str(port),
+        "--log-level", "info",
+    ]
+
+    with open(log_file, "a") as log:
+        log.write(f"\n--- ObsiGate started at {time.ctime()} ---\n")
+        proc = subprocess.Popen(cmd, cwd=BACKEND_DIR, stdout=log, stderr=log)
+
+        def handle_signal(signum, frame):
+            print("Shutting down ObsiGate backend...")
+            proc.terminate()
+            proc.wait(timeout=10)
+            sys.exit(0)
+
+        signal.signal(signal.SIGTERM, handle_signal)
+        signal.signal(signal.SIGINT, handle_signal)
+
+        # Wait for backend to finish
+        proc.wait()
+
+
+if __name__ == "__main__":
+    main()