Extracts the docker-exec-with-base64-stdin pattern out of canary/planter
and orchestrator/drivers/ssh into a shared decnet.decky_io package.
Both consumers now delegate; the canary planter test still proves the
contract end-to-end.
Adds POST/DELETE /api/v1/deckies/files for arbitrary file drops.
Container resolution is shared with the canary path: topology_id absent
means fleet (<name>-ssh), present routes through resolve_decky_container
which picks <name>-ssh when the topology decky exposes ssh, else the
topology base container decnet_t_<id8>_<name>.
Path validation rejects relative paths and '..' traversal at the request
model layer. Bad base64 → 400; unknown topology → 404; decky not in
topology → 422; docker exec failure → 409.
POST /api/v1/canary/tokens grows an optional topology_id field. When
present, the server hydrates the topology, validates the named decky is
in it, and resolves the docker container via
planter.resolve_topology_container — <name>-ssh if the decky exposes ssh,
else the topology base container. Absent ⇒ fleet semantics, unchanged.
The token row gets a nullable topology_id column (no migration helper
per pre-v1 policy). GET /api/v1/canary/tokens accepts ?topology_id= as
a filter. DELETE re-resolves the container at revoke time so a
redeployed topology is still reachable.
422 when the named decky isn't in the topology; 404 when the topology
itself doesn't exist.
