GET /computes/{id} answered with only part of the capabilities the compute
reports: the response schema kept a second, private Capabilities class of
its own (it knew ubridge_tc and nothing else), and FastAPI's response model
silently drops fields it does not define — so ubridge_tap and
ubridge_iol_tap never reached clients even though the compute had sent
them and links were already being built on those datapaths.
Import the one definition instead of duplicating it, so the next capability
cannot drift the same way.
The compute_get/compute_images MCP tools typed compute_id as a UUID, so
passing 'local' (the actual id of the built-in compute, which the
compute_images description itself pointed to) was rejected by schema
validation. Both tools now take a string defaulting to 'local', and the
compute_get REST route resolves 'local' through the controller since the
local compute has no database entry.
