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)).

cli.py

@@ -1396,7 +1396,7 @@ def _detect_light_mode() -> bool:
             last = cfgbg.split(";")[-1] if ";" in cfgbg else cfgbg
             if last.isdigit():
                 bg = int(last)
-                if bg in (7, 15):
+                if bg in {7, 15}:
                     result = True
                     _LIGHT_MODE_CACHE = result
                     return result
@@ -7706,7 +7706,7 @@ class HermesCLI:
             # google-gemini/gemini-cli#19332.
             _rest = cmd_original.split(None, 1)
             _args = (_rest[1] if len(_rest) > 1 else "").strip().lower()
-            if _args in ("--delete", "-d"):
+            if _args in {"--delete", "-d"}:
                 self._delete_session_on_exit = True
             elif _args:
                 _cprint(f"  {_DIM}✗ Unknown argument: {_escape(_args)}. Use /exit --delete to also remove session history.{_RST}")
@@ -13835,7 +13835,7 @@ class HermesCLI:
             if _errno == errno.EIO:
                 pass  # suppress broken-stdout I/O errors on interrupt (#13710)
             elif (
-                _errno in (errno.EINVAL, errno.EBADF)
+                _errno in {errno.EINVAL, errno.EBADF}
                 or "is not registered" in _msg
                 or "Bad file descriptor" in _msg
                 or "Invalid argument" in _msg