Add seeded task workspace creation

Current persistent tasks started with an empty workspace, which blocked the first useful host-to-task workflow in the task roadmap. This change lets task creation start from a host directory or tar archive without changing the one-shot VM surfaces.

Expose source_path on task create across the CLI, SDK, and MCP, add safe archive upload and extraction support for guest and host-compat backends, persist workspace_seed metadata, and patch the per-task rootfs with the bundled guest agent before boot so seeded guest tasks work without republishing environments. Also switch post--- command reconstruction to shlex.join() so documented sh -lc task examples preserve argument boundaries.

Validation:
- uv lock
- UV_CACHE_DIR=.uv-cache uv run pytest --no-cov tests/test_vm_guest.py tests/test_vm_manager.py tests/test_cli.py tests/test_api.py tests/test_server.py tests/test_public_contract.py
- UV_CACHE_DIR=.uv-cache make check
- UV_CACHE_DIR=.uv-cache make dist-check
- real guest-backed smoke: task create --source-path, task exec -- cat note.txt, task delete

tests/test_server.py

@@ -171,6 +171,9 @@ def test_task_tools_round_trip(tmp_path: Path) -> None:
         base_dir=tmp_path / "vms",
         network_manager=TapNetworkManager(enabled=False),
     )
+    source_dir = tmp_path / "seed"
+    source_dir.mkdir()
+    (source_dir / "note.txt").write_text("ok\n", encoding="utf-8")
 
     def _extract_structured(raw_result: object) -> dict[str, Any]:
         if not isinstance(raw_result, tuple) or len(raw_result) != 2:
@@ -188,6 +191,7 @@ def test_task_tools_round_trip(tmp_path: Path) -> None:
                 {
                     "environment": "debian:12-base",
                     "allow_host_compat": True,
+                    "source_path": str(source_dir),
                 },
             )
         )
@@ -197,7 +201,7 @@ def test_task_tools_round_trip(tmp_path: Path) -> None:
                 "task_exec",
                 {
                     "task_id": task_id,
-                    "command": "printf 'ok\\n'",
+                    "command": "cat note.txt",
                 },
             )
         )
@@ -207,6 +211,7 @@ def test_task_tools_round_trip(tmp_path: Path) -> None:
 
     created, executed, logs, deleted = asyncio.run(_run())
     assert created["state"] == "started"
+    assert created["workspace_seed"]["mode"] == "directory"
     assert executed["stdout"] == "ok\n"
     assert logs["count"] == 1
     assert deleted["deleted"] is True