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)).

plugins/google_meet/tools.py

@@ -36,7 +36,7 @@ def check_meet_requirements() -> bool:
     handlers relax the requirement when a node is addressed.
     """
     import platform as _p
-    if _p.system().lower() not in ("linux", "darwin"):
+    if _p.system().lower() not in {"linux", "darwin"}:
         return False
     try:
         import playwright  # noqa: F401
@@ -238,7 +238,7 @@ def handle_meet_join(args: Dict[str, Any], **_kw) -> str:
     if not url:
         return _err("url is required")
     mode = (args.get("mode") or "transcribe").strip().lower()
-    if mode not in ("transcribe", "realtime"):
+    if mode not in {"transcribe", "realtime"}:
         return _err(f"mode must be 'transcribe' or 'realtime' (got {mode!r})")
 
     node = args.get("node")