Turnstone container-VM: podman image -> boco qcow2 boot

Arch image with turnstone (venv), dev toolkit, rootless podman; boots
via boco (virtiofs shares, direct UID mapping for nested virtiofs).
sshd ops channel + turnstone-server as guest marvin; state (SQLite db,
config, work) on host shares; LLM via the TensorX OpenAI-compatible
gateway (https://api.tensorx.ai/v1), reachable from the guest through
both slirp layers with no relay.

.dockerignore

@@ -0,0 +1,10 @@
+# Keep build context minimal; authorized_keys is COPY'd in, the private
+# key must never enter the image.
+.git
+data
+work
+scripts
+README.md
+configs/ssh/id_ed25519
+configs/ssh/id_ed25519.pub
+configs/turnstone/config.toml