task: fold infrahubctl marketplace CLI back onto shared ctl conventions

[dgarros]

Need

infrahub_sdk/ctl/marketplace.py (~700 lines, 4 commands) has grown into an
architectural island within infrahubctl. It diverges from the shared CLI
conventions documented in infrahub_sdk/ctl/AGENTS.md on several axes:

• Client — builds a raw httpx.AsyncClient via its own _make_http_client()
  (re-deriving proxy/TLS config from the SDK config) instead of the shared
  initialize_client(). initialize_client is never imported here.
• Error handling — ships a parallel error framework (_ErrorClass, _fail(),
  _classify_http_error(), _fail_http_error()) alongside the shared
  catch_exception / handle_exception in ctl/utils.py.
• Output — defines its own console / err_console (Console(stderr=True))
  stderr channel rather than the shared console pattern.

The result is effectively a mini-app: contributors touching marketplace commands
have to learn a second set of patterns, fixes to the shared client/error layer
do not reach it, and the divergence quietly undercuts the conventions the rest of
the CLI (and ctl/AGENTS.md) rely on.

Context

• The file already imports and uses the shared catch_exception decorator, so it
  is only partially integrated — the two systems currently coexist.
• Some divergence may be justified (e.g. the marketplace talks to public
  /api/v1/... endpoints that may not require an authenticated Infrahub client);
  scoping which parts should converge vs. stay bespoke is part of the work.

References

• Convention this diverges from: infrahub_sdk/ctl/AGENTS.md (Command Pattern)
• Related marketplace work: feature: add --dependencies flag to infrahubctl marketplace get for automatic collection dependency resolution #1117