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/gateway/test_platform_connected_checkers.py

@@ -76,12 +76,12 @@ def test_checker_returns_true_when_configured(platform, checker, monkeypatch):
     elif platform == Platform.SMS:
         monkeypatch.setenv("TWILIO_ACCOUNT_SID", "ACtest")
         mock_config.extra = {}
-    elif platform in (
+    elif platform in {
         Platform.API_SERVER,
         Platform.WEBHOOK,
         Platform.MSGRAPH_WEBHOOK,
         Platform.WHATSAPP,
-    ):
+    }:
         mock_config.extra = {}
     elif platform == Platform.FEISHU:
         mock_config.extra = {"app_id": "app"}