fix(tests): fix integration test failures from deprecated git key, missing wget, and wrong prompt path

- test_sandbox_escape: migrate manifest fixture from deprecated `git`
  key to `git-gate` (PRD 0047) — `remotes` → `repos`, field names
  `Name`/`Upstream`/`IdentityFile` → `url`/`identity`
- test_smolmachines_launch probes: replace `wget` (not in node:22-slim)
  with `curl -s --show-error --max-time 3` (installed in Dockerfile.claude)
- test_smolmachines_launch prompt test: correct path /root/ → /home/node/
  to match guest_home in smolmachines/prepare.py

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

tests/integration/test_sandbox_escape.py

@@ -120,11 +120,10 @@ class TestSandboxEscape(unittest.TestCase):
                     # is intentionally unreachable — the pre-receive
                     # gitleaks hook must reject BEFORE git-gate
                     # attempts the upstream push.
-                    "git": {"remotes": {
-                        "unreachable.invalid": {
-                            "Name": "throwaway",
-                            "Upstream": "ssh://git@unreachable.invalid:22/throwaway.git",
-                            "IdentityFile": str(cls._key_path),
+                    "git-gate": {"repos": {
+                        "throwaway": {
+                            "url": "ssh://git@unreachable.invalid:22/throwaway.git",
+                            "identity": str(cls._key_path),
                         },
                     }},
                 },