refactor: extract pydantic schemas from routers into schemas/ directory (Task 3.2)

- Create schemas/ directory with 12 schema files covering all domains
- Extract 70+ Pydantic models from 11 router files
- Routers now import from src.schemas.{domain} instead of defining inline
- Zero inline BaseModel definitions remain in any router

Quality gates: py_compile all schemas (pass), py_compile all routers (pass)
Refs: repo-restructure Task 3.2

apps/web/src/main.tsx

@@ -11,13 +11,13 @@ import "./styles/utilities.css";
 import "./styles/syntax-highlight.css";
 
 ReactDOM.createRoot(document.getElementById("root")!).render(
-  <React.StrictMode>
-    <BrowserRouter>
-      <AuthProvider>
-        <SessionsProvider>
-          <AppRouter />
-        </SessionsProvider>
-      </AuthProvider>
-    </BrowserRouter>
-  </React.StrictMode>
+	<React.StrictMode>
+		<BrowserRouter>
+			<AuthProvider>
+				<SessionsProvider>
+					<AppRouter />
+				</SessionsProvider>
+			</AuthProvider>
+		</BrowserRouter>
+	</React.StrictMode>,
 );