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/tools/test_browser_homebrew_paths.py

@@ -68,10 +68,10 @@ class TestDiscoverHomebrewNodeDirs:
             if p == "/opt/homebrew/opt":
                 return True
             # node@20/bin and node@24/bin exist
-            if p in (
+            if p in {
                 "/opt/homebrew/opt/node@20/bin",
                 "/opt/homebrew/opt/node@24/bin",
-            ):
+            }:
                 return True
             return False
 
@@ -171,10 +171,10 @@ class TestFindAgentBrowser:
         real_isdir = os.path.isdir
 
         def selective_isdir(path):
-            if path in (
+            if path in {
                 "/data/data/com.termux/files/usr/bin",
                 "/data/data/com.termux/files/usr/sbin",
-            ):
+            }:
                 return True
             return real_isdir(path)
 
@@ -486,10 +486,10 @@ class TestRunBrowserCommandPathConstruction:
         real_isdir = os.path.isdir
 
         def selective_isdir(path):
-            if path in (
+            if path in {
                 "/data/data/com.termux/files/usr/bin",
                 "/data/data/com.termux/files/usr/sbin",
-            ):
+            }:
                 return True
             if path.startswith(str(tmp_path)):
                 return True