feat: interactive terminal — WS-bridged docker exec PTY

GET /services/:id/terminal upgrades to a WebSocket attached to a
`docker exec` PTY in the service's running replica. JSON frames both
ways: stdin/resize out, stdout/exit/error in. Shell probe tries each
candidate (bash→sh) since `command -v` needs a shell to run; distroless
images get a clean "no shell" error instead of an OCI failure dump.

- docker.Client gains ExecAttach + ExecResize wrappers
- Frontend: xterm.js replaces the one-off console section — live PTY,
  fit-addon resizes forwarded over the socket
- CLI: `containr shell <id>` bridges the local TTY (raw mode, SIGWINCH
  resize forwarding); `containr exec` keeps the one-off command path
- Access mirrors service logs: project manage scope required

Generated with [Devin](https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

app/frontend/package-lock.json

@@ -33,6 +33,8 @@
         "@tailwindcss/typography": "^0.5.19",
         "@tanstack/react-query": "^5.66.0",
         "@types/dompurify": "^3.0.5",
+        "@xterm/addon-fit": "^0.11.0",
+        "@xterm/xterm": "^6.0.0",
         "@xyflow/react": "^12.10.0",
         "autoprefixer": "^10.4.24",
         "axios": "^1.7.9",
@@ -4262,6 +4264,21 @@
         "url": "https://opencollective.com/vitest"
       }
     },
+    "node_modules/@xterm/addon-fit": {
+      "version": "0.11.0",
+      "resolved": "https://registry.npmjs.org/@xterm/addon-fit/-/addon-fit-0.11.0.tgz",
+      "integrity": "sha512-jYcgT6xtVYhnhgxh3QgYDnnNMYTcf8ElbxxFzX0IZo+vabQqSPAjC3c1wJrKB5E19VwQei89QCiZZP86DCPF7g==",
+      "license": "MIT"
+    },
+    "node_modules/@xterm/xterm": {
+      "version": "6.0.0",
+      "resolved": "https://registry.npmjs.org/@xterm/xterm/-/xterm-6.0.0.tgz",
+      "integrity": "sha512-TQwDdQGtwwDt+2cgKDLn0IRaSxYu1tSUjgKarSDkUM0ZNiSRXFpjxEsvc/Zgc5kq5omJ+V0a8/kIM2WD3sMOYg==",
+      "license": "MIT",
+      "workspaces": [
+        "addons/*"
+      ]
+    },
     "node_modules/@xyflow/react": {
       "version": "12.10.1",
       "resolved": "https://registry.npmjs.org/@xyflow/react/-/react-12.10.1.tgz",