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)).

skills/creative/comfyui/scripts/_common.py

@@ -592,7 +592,7 @@ def _http_once(
                 # Build a new request with cleaned headers
                 clean_headers = {
                     k: v for k, v in req2.header_items()
-                    if k.lower() not in ("x-api-key", "authorization", "cookie")
+                    if k.lower() not in {"x-api-key", "authorization", "cookie"}
                 }
                 new_req = urllib.request.Request(newurl, headers=clean_headers, method="GET")
                 return new_req
@@ -743,13 +743,13 @@ def safe_path_join(base: Path, *parts: str) -> Path:
 
 def media_type_from_filename(filename: str) -> str:
     ext = Path(filename).suffix.lower()
-    if ext in (".mp4", ".webm", ".avi", ".mov", ".mkv", ".gif", ".webp"):
+    if ext in {".mp4", ".webm", ".avi", ".mov", ".mkv", ".gif", ".webp"}:
         return "video"
-    if ext in (".wav", ".mp3", ".flac", ".ogg", ".m4a"):
+    if ext in {".wav", ".mp3", ".flac", ".ogg", ".m4a"}:
         return "audio"
-    if ext in (".glb", ".obj", ".ply", ".gltf"):
+    if ext in {".glb", ".obj", ".ply", ".gltf"}:
         return "3d"
-    if ext in (".json", ".txt", ".md"):
+    if ext in {".json", ".txt", ".md"}:
         return "text"
     return "image"