chore: ruff auto-fix PLR6201 resweep — tuple → set in membership tests (#27355)

Six days after #23937 (608 fixes) the codebase had accumulated 241 new
PLR6201 violations. Same mechanical `x in (...)` → `x in {...}` fix,
same zero-risk profile: set lookup is O(1) vs O(n) for tuple and the
two are semantically equivalent for hashable scalar membership tests.

All 241 instances fixed via `ruff check --select PLR6201 --fix
--unsafe-fixes`, zero remaining. Every changed value is a hashable
scalar (str/int/None/enum/signal); no risk of unhashable runtime
errors. No behavior change.

Test plan:
- 119 files changed, +244/-244 (net zero) — exactly one-line edits
- `ruff check` clean afterward
- Compile checks pass on the largest touched files (cli.py, run_agent.py,
  gateway/run.py, gateway/platforms/discord.py, model_tools.py)
- Subset broad test run on tests/gateway/ tests/hermes_cli/ tests/agent/
  tests/tools/: 18187 passed, 59 pre-existing failures (verified against
  origin/main with the same shape — identical failure count, identical
  category — all xdist test-order flakes unrelated to this change)

Follows the same template as PR #23937 ([tracker: #23972](https://github.com/NousResearch/hermes-agent/issues/23972)).

tests/hermes_cli/test_models.py

@@ -252,7 +252,7 @@ class TestDetectProviderForModel:
         result = detect_provider_for_model("deepseek-chat", "openai-codex")
         assert result is not None
         # Provider is deepseek (direct) or openrouter (fallback) depending on creds
-        assert result[0] in ("deepseek", "openrouter")
+        assert result[0] in {"deepseek", "openrouter"}
 
     def test_current_provider_model_returns_none(self):
         """Models belonging to the current provider should not trigger a switch."""
@@ -302,7 +302,7 @@ class TestDetectProviderForModel:
         with patch("hermes_cli.models.fetch_openrouter_models", return_value=LIVE_OPENROUTER_MODELS):
             result = detect_provider_for_model("claude-opus-4-6", "openai-codex")
         assert result is not None
-        assert result[0] not in ("nous",)  # nous has claude models but shouldn't be suggested
+        assert result[0] not in {"nous",}  # nous has claude models but shouldn't be suggested
 
 
 class TestIsNousFreeTier: