feat: improve session naming, project display, rename support, tab titles

Backend:
- sessions.py: include workspace_name in session response
- instance_service.py: auto-generate display names as
  'Project / Workspace / Tool #N' instead of 'Workspace / Tool #N'
- instance_service.py: add rename_tool_instance() service function
- tool_instances.py: add PATCH /instances/{id} endpoint for renaming
  display_name

Frontend:
- api/sessions.ts: add workspace_name to Session type, add renameInstance()
- use-instance-actions.ts: add handleRename, set document.title when opening
- session-card.tsx: click-to-edit display_name inline; always show project
  context line (Project / Workspace or Repo / Tool)
- session-list.tsx: pass through onRename prop
- SessionsPage.tsx: wire handleRename to SessionCard and SessionList
- app-shell.tsx: sidebar tooltip includes workspace or repo name
- use-terminal-page.ts: set document.title based on active terminal session

Quality gates: py_compile all backend files pass, tsc --noEmit pass,
npm run build pass, 82/82 tests pass

apps/web/src/hooks/use-instance-actions.ts

@@ -4,6 +4,7 @@ import {
 	deleteInstance,
 	startInstance,
 	recreateInstanceTunnel,
+	renameInstance,
 } from "../api/sessions";
 import type { Session } from "../api/sessions";
 
@@ -21,6 +22,7 @@ interface UseInstanceActionsReturn {
 	handleDelete: (session: Session) => Promise<void>;
 	handleForceDelete: (session: Session) => Promise<void>;
 	handleRecreateTunnel: (session: Session) => Promise<void>;
+	handleRename: (session: Session, newName: string) => Promise<void>;
 	clearDirtyDelete: () => void;
 }
 
@@ -52,6 +54,7 @@ export function useInstanceActions(
 			url = `/projects/${session.project_id}`;
 		}
 
+		document.title = `${session.display_name} — Headquarter`;
 		const w = window.open(url, `session-${session.id}`);
 		tabRefs.current.set(key, w);
 	}, []);
@@ -177,6 +180,27 @@ export function useInstanceActions(
 		[loadingSessionId, onRefresh],
 	);
 
+	const handleRename = useCallback(
+		async (session: Session, newName: string) => {
+			if (!newName.trim()) return;
+			setLoadingSessionId(session.id);
+			try {
+				await renameInstance(
+					session.project_id,
+					session.repository_id,
+					session.id,
+					newName.trim(),
+				);
+				await onRefresh();
+			} catch {
+				// ignore
+			} finally {
+				setLoadingSessionId(null);
+			}
+		},
+		[onRefresh],
+	);
+
 	const clearDirtyDelete = useCallback(() => {
 		setDirtyDeleteSession(null);
 		setDirtyDeleteFiles([]);
@@ -192,6 +216,7 @@ export function useInstanceActions(
 		handleDelete,
 		handleForceDelete,
 		handleRecreateTunnel,
+		handleRename,
 		clearDirtyDelete,
 	};
 }