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)).

run_agent.py

@@ -1365,7 +1365,7 @@ class AIAgent:
         the existing 1M-context-beta branch handles them; revisit if other
         subscription tiers start producing the same loop signature).
         """
-        if status_code not in (401, 403, None):
+        if status_code not in {401, 403, None}:
             return False
         if not isinstance(error_context, dict):
             return False
@@ -1774,7 +1774,7 @@ class AIAgent:
             import os as _os
             env = _os.environ.get("HERMES_FILE_MUTATION_VERIFIER")
             if env is not None:
-                return env.strip().lower() not in ("0", "false", "no", "off")
+                return env.strip().lower() not in {"0", "false", "no", "off"}
             # Read from the persisted config.yaml so gateway and CLI share
             # the same setting.  Import lazily to avoid a startup-time cycle.
             try: