chore: remove unused imports and dead locals (ruff F401, F841) (#17010)

Mechanical cleanup across 43 files — removes 46 unused imports
(F401) and 14 unused local variables (F841) detected by
`ruff check --select F401,F841`. Net: -49 lines.

Also fixes a latent NameError in rl_cli.py where `get_hermes_home()`
was called at module line 32 before its import at line 65 — the
module never imported successfully on main. The ruff audit surfaced
this because it correctly saw the symbol as imported-but-unused
(the call happened before the import ran); the fix moves the import
to the top of the file alongside other stdlib imports.

One `# noqa: F401` kept in hermes_cli/status.py for `subprocess`:
tests monkeypatch `hermes_cli.status.subprocess` as a regression
guard that systemctl isn't called on Termux, so the name must
exist at module scope even though the module body doesn't reference
it. Docstring explains the reason.

Also fixes an invalid `# noqa:` directive in
gateway/platforms/discord.py:308 that lacked a rule code.

Co-authored-by: teknium1 <teknium@users.noreply.github.com>

tools/browser_tool.py

@@ -526,7 +526,6 @@ def _url_is_private(url: str) -> bool:
     backend is configured, which will surface the DNS error naturally).
     """
     try:
-        from tools.url_safety import is_safe_url
         # is_safe_url returns False for private/loopback/link-local/CGNAT AND
         # for DNS failures.  We only want the private-network case here, so
         # we parse + check the host shape as a DNS-failure sieve first.