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/agent/lsp/_mock_lsp_server.py

@@ -91,7 +91,7 @@ def main():
         if msg.get("method") == "workspace/didChangeWatchedFiles":
             continue
 
-        if msg.get("method") in ("textDocument/didOpen", "textDocument/didChange"):
+        if msg.get("method") in {"textDocument/didOpen", "textDocument/didChange"}:
             params = msg.get("params") or {}
             td = params.get("textDocument") or {}
             uri = td.get("uri", "")

tests/agent/lsp/test_install_and_lint_fixes.py

@@ -87,10 +87,10 @@ def test_install_npm_works_without_extras(tmp_path, monkeypatch):
     cmd = captured["cmd"]
     assert "pyright" in cmd
     # Should not blow up when extra_pkgs is omitted/None
-    install_targets = [c for c in cmd if not c.startswith("-") and c not in (
+    install_targets = [c for c in cmd if not c.startswith("-") and c not in {
         "install", "--prefix", str(install_mod.hermes_lsp_bin_dir().parent),
         "/usr/bin/npm",
-    )]
+    }]
     assert install_targets == ["pyright"]