feat(agy-cli): register agy-cli provider in auth registry + runtime resolver

[arminanton]

Summary

Registers the agy-cli (Antigravity CLI) provider in the two core auth/runtime seams, so the agy-cli model provider is wired into Hermes' resolution path. This is the auth/runtime registration half of the agy-cli provider; the client (agent/agy_cli_client.py), plugin, and tests live in the sibling PR #50555.

Changes (+27 lines, 2 files)

1. hermes_cli/auth.py — adds the agy-cli entry to PROVIDER_REGISTRY:

   "agy-cli": ProviderConfig(
       id="agy-cli",
       name="Antigravity CLI (agy)",
       auth_type="external_process",
       inference_base_url="agy://antigravity",   # internal marker, never sent over HTTP
       base_url_env_var="HERMES_AGY_COMMAND",
   ),

2. hermes_cli/runtime_provider.py — adds the if provider == "agy-cli": branch in resolve_runtime_provider(), mirroring the existing copilot-acp external-process pattern. Returns api_mode="agy_cli" + the marker base_url so init_agent routes to AgyCliClient. Auth is fully internal to the agy binary (its own OAuth/cloudcode-pa session), so there's nothing for Hermes to resolve.

Verification

• Applies clean on current main (+27 lines).
• Compiles; 0 new test failures (the 39 pre-existing tests/hermes_cli/ failures are identical with and without this change — they're upstream environment/isolation issues, not from this PR).
• Functional: resolve_runtime_provider(requested="agy-cli") → api_mode='agy_cli', base_url='agy://antigravity'; PROVIDER_REGISTRY["agy-cli"].auth_type == "external_process".

Relationship to #50555

#50555 carries the agy-cli client + plugin + tests (currently a stale-base WIP draft). This PR carries the small, current-main-clean auth/runtime registration that #50555's stale base can't host without a rebase. The two together complete the agy-cli provider; they can be consolidated at #50555's upgrade.

Draft (agy-cli is WIP per the project's isolate-agy-cli policy).

[alt-glitch]

Related: this is the auth/runtime-registration half of the agy-cli (Antigravity CLI) provider; the client + plugin + tests live in the sibling draft #50555. Earlier whole-provider draft #50039 is now closed. Part of the Gemini-CLI-consumer-sunset remediation family (#29294). Not a duplicate — intentional same-author split so the small current-main-clean registration can land independently of #50555's stale base.

[arminanton]

Withdrawing — this is the auth/runtime-registration half of the agy-cli provider whose client lives in #50555, now closed. The agy-cli direction is superseded by the merged native google-antigravity provider (#50454), and the whole Google-OAuth inference category was then removed by #50492 for account-ban safety. No agy registration to land. Thanks.