fix(models): delist hy3-free and laguna-s-2.1-free — OpenCode relay dropped them (anon 401)

The OpenCode Zen relay no longer serves hy3-free (since ~2026-08-31) or
laguna-s-2.1-free (new, verified 2026-09-09): both are gone from the live
GET /zen/v1/models catalog and anonymous chat completions return
401 {"type":"ModelError","message":"Model <id> is not supported"}
(2 probes >=60s apart, x-opencode-session header present).

- hermes_cli/models_catalog_static.py: remove both slugs from the
  opencode-free offline floor and the opencode-zen discovery floor;
  document the delist dates in the catalog comment.
- plugins/model-providers/opencode-free: default_aux_model moves from the
  dead laguna-s-2.1-free to nemotron-3.5-lightning-free (fastest surviving
  anonymous model).
- tests: swap fixtures off the dead slugs; extend the floor-exclusion
  invariant to cover both.

The live revalidation path already hides them when the relay is reachable;
this fixes the OFFLINE floor and the aux default, which would otherwise
offer/route to models that 401.

plugins/model-providers/opencode-free/__init__.py

@@ -40,9 +40,10 @@ opencode_free = OpenCodeFreeProfile(
         "X-Title": "Hermes Agent",
         "User-Agent": f"HermesAgent/{_HERMES_VERSION}",
     },
-    # laguna is the fastest non-UA-gated free model; big-pickle 429s every
+    # laguna-s-2.1-free was delisted by the relay 2026-09-09 (anon 401); the fastest
+    # surviving free model is the lightning-tier Nemotron. big-pickle 429s every
     # client except the opencode CLI's own User-Agent.
-    default_aux_model="laguna-s-2.1-free",
+    default_aux_model="nemotron-3.5-lightning-free",
 )
 
 register_provider(opencode_free)