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/tui_gateway/test_entry_sys_path.py

@@ -25,7 +25,7 @@ def _reload_entry_with_env(env_overrides: dict) -> None:
             _src_root = os.environ.get("HERMES_PYTHON_SRC_ROOT", "")
             if _src_root and _src_root not in sys.path:
                 sys.path.insert(0, _src_root)
-            sys.path = [p for p in sys.path if p not in ("", ".")]
+            sys.path = [p for p in sys.path if p not in {"", "."}]
         return sys.path[:]
     finally:
         sys.path = original_path
@@ -45,7 +45,7 @@ def test_empty_string_and_dot_removed_from_sys_path():
         assert "." in sys.path
 
         # Run the entry.py fixup logic directly
-        sys.path = [p for p in sys.path if p not in ("", ".")]
+        sys.path = [p for p in sys.path if p not in {"", "."}]
 
         assert "" not in sys.path
         assert "." not in sys.path
@@ -61,7 +61,7 @@ def test_hermes_src_root_inserted_at_front():
             _src_root = os.environ.get("HERMES_PYTHON_SRC_ROOT", "")
             if _src_root and _src_root not in sys.path:
                 sys.path.insert(0, _src_root)
-            sys.path = [p for p in sys.path if p not in ("", ".")]
+            sys.path = [p for p in sys.path if p not in {"", "."}]
 
         assert sys.path[0] == fake_root
     finally:
@@ -79,7 +79,7 @@ def test_src_root_not_duplicated_if_already_present():
             _src_root = os.environ.get("HERMES_PYTHON_SRC_ROOT", "")
             if _src_root and _src_root not in sys.path:
                 sys.path.insert(0, _src_root)
-            sys.path = [p for p in sys.path if p not in ("", ".")]
+            sys.path = [p for p in sys.path if p not in {"", "."}]
 
         assert sys.path.count(fake_root) == count_before
     finally:
@@ -95,7 +95,7 @@ def test_no_src_root_env_does_not_crash():
             _src_root = os.environ.get("HERMES_PYTHON_SRC_ROOT", "")
             if _src_root and _src_root not in sys.path:
                 sys.path.insert(0, _src_root)
-            sys.path = [p for p in sys.path if p not in ("", ".")]
+            sys.path = [p for p in sys.path if p not in {"", "."}]
         # No exception raised
     finally:
         sys.path = original