refactor: pivot from ssh proxy to distributed api model

- Delete SSHFileAdapter, IFileAdapter, LocalFileAdapter (SSH/SFTP stack)
- Remove ssh2, ssh2-sftp-client dependencies; add http-proxy-middleware, http-proxy
- NodeRegistry: remote nodes no longer use Dockerode TCP; new getProxyTarget() returns {apiUrl, apiToken}
- NodeRegistry.testConnection: remote nodes use HTTP GET /api/auth/check instead of docker.info()
- DatabaseService: Node interface swaps SSH/TLS fields for api_url + api_token; legacy columns preserved for DB compat
- FileSystemService: reverted to clean local-only fs.promises; adapter pattern fully removed
- ComposeService: executeRemote() and SSH log streaming deleted; local-only execution remains
- index.ts: add /api/auth/generate-node-token endpoint (long-lived JWT, scope:node_proxy)
- index.ts: authMiddleware now accepts Bearer token in addition to cookie (Sencho-to-Sencho auth)
- index.ts: remote HTTP proxy middleware intercepts all /api/ requests for remote nodes, strips x-node-id, injects Authorization header, proxies to api_url
- index.ts: WS upgrade handler proxies WebSocket connections for remote nodes via http-proxy wsProxyServer
- NodeManager.tsx: form reduced to Name, API URL, API Token; Generate Node Token button added inline
- NodeContext.tsx: Node interface updated to api_url/api_token

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/package.json

@@ -17,10 +17,9 @@
     "@types/bcrypt": "^6.0.0",
     "@types/better-sqlite3": "^7.6.13",
     "@types/cookie-parser": "^1.4.10",
+    "@types/http-proxy-middleware": "^0.19.3",
     "@types/jsonwebtoken": "^9.0.10",
     "@types/node": "^25.3.0",
-    "@types/ssh2": "^1.15.5",
-    "@types/ssh2-sftp-client": "^9.0.6",
     "@types/yaml": "^1.9.6",
     "nodemon": "^3.1.13",
     "ts-node": "^10.9.2",
@@ -30,6 +29,7 @@
     "@types/cors": "^2.8.19",
     "@types/dockerode": "^4.0.1",
     "@types/express": "^5.0.6",
+    "@types/http-proxy": "^1.17.17",
     "@types/ws": "^8.18.1",
     "axios": "^1.13.6",
     "bcrypt": "^6.0.0",
@@ -39,10 +39,10 @@
     "cors": "^2.8.6",
     "dockerode": "^4.0.9",
     "express": "^5.2.1",
+    "http-proxy": "^1.18.1",
+    "http-proxy-middleware": "^3.0.5",
     "jsonwebtoken": "^9.0.3",
     "node-pty": "^1.1.0",
-    "ssh2": "^1.17.0",
-    "ssh2-sftp-client": "^12.1.0",
     "systeminformation": "^5.31.1",
     "ws": "^8.19.0",
     "yaml": "^2.8.2"