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>

hermes_cli/web_server.py

@@ -736,7 +736,7 @@ async def get_sessions(limit: int = 20, offset: int = 0):
             return {"sessions": sessions, "total": total, "limit": limit, "offset": offset}
         finally:
             db.close()
-    except Exception as e:
+    except Exception:
         _log.exception("GET /api/sessions failed")
         raise HTTPException(status_code=500, detail="Internal server error")
 
@@ -968,7 +968,7 @@ async def update_config(body: ConfigUpdate):
     try:
         save_config(_denormalize_config_from_web(body.config))
         return {"ok": True}
-    except Exception as e:
+    except Exception:
         _log.exception("PUT /api/config failed")
         raise HTTPException(status_code=500, detail="Internal server error")
 
@@ -997,7 +997,7 @@ async def set_env_var(body: EnvVarUpdate):
     try:
         save_env_value(body.key, body.value)
         return {"ok": True, "key": body.key}
-    except Exception as e:
+    except Exception:
         _log.exception("PUT /api/env failed")
         raise HTTPException(status_code=500, detail="Internal server error")
 
@@ -1011,7 +1011,7 @@ async def remove_env_var(body: EnvVarDelete):
         return {"ok": True, "key": body.key}
     except HTTPException:
         raise
-    except Exception as e:
+    except Exception:
         _log.exception("DELETE /api/env failed")
         raise HTTPException(status_code=500, detail="Internal server error")
 
@@ -1568,7 +1568,6 @@ async def _start_device_code_flow(provider_id: str) -> Dict[str, Any]:
     then spawns a background poller. Returns the user-facing display fields
     so the UI can render the verification page link + user code.
     """
-    from hermes_cli import auth as hauth
     if provider_id == "nous":
         from hermes_cli.auth import _request_device_code, PROVIDER_REGISTRY
         import httpx