style: fix all ruff and eslint errors across codebase

Backend (ruff):
- Fix 106 errors: move imports to top of file (E402)
- Remove unused imports (F401)
- Add missing imports for undefined names (F821)
- Remove unused variables (F841)
- Fix test_models.py broken RefreshToken test
- Fix test_projects_api.py missing TestClient import

Frontend (eslint):
- Remove unused imports/variables across 10 files
- Fix explicit any types in client.ts and sessions.ts
- Clean up empty block statements in terminal.tsx

Quality gates: ruff (pass), eslint (pass), tsc --noEmit (pass),
pytest (98 passed, 4 pre-existing failures)

apps/web/src/pages/sessions.tsx

@@ -1,5 +1,4 @@
 import { useCallback, useEffect, useMemo, useState } from "react";
-import { useNavigate } from "react-router-dom";
 
 import { listProjects } from "../api/projects";
 import type { Project } from "../types";
@@ -11,7 +10,7 @@ import {
 } from "../api/sessions";
 import { listToolTypes, type ToolType } from "../api/tool_types";
 import { getUserConfig, updateUserConfig } from "../api/settings";
-import { EmptyState, ErrorState, LoadingState } from "../components/data-states";
+import { ErrorState, LoadingState } from "../components/data-states";
 import { CreateSessionForm } from "../components/create-session-form";
 import { SessionList } from "../components/session-list";
 import { SessionCard } from "../components/session-card";
@@ -21,7 +20,6 @@ import type { InstanceHealth } from "../api/sessions";
 type SessionsStatus = "loading" | "ready" | "error";
 
 export const SessionsPage = () => {
-  const navigate = useNavigate();
   const [status, setStatus] = useState<SessionsStatus>("loading");
   const [sessions, setSessions] = useState<Session[]>([]);
   const [lastSessionId, setLastSessionId] = useState<string | null>(null);