feat(kanban): deadlines en cards (context menu, badges, calendario, history)

- migration 009 + columna deadline TEXT en cards
- backend: CardPatch.HasDeadline, eventos deadline_set/deadline_cleared
- KanbanCard: menu derecho con DatePicker, badge countdown con colores por ratio (azul>=50%, amarillo<50%, rojo<10%, red.9 overdue)
- App.tsx: filtro "Con deadline", handleSetCardDeadline optimista, jump-to-card + highlight
- CalendarView: popover por dia con seq_num + titulo, click navega a card en tablero
- HistoryModal: render eventos deadline_set/deadline_cleared
- .gitignore: *.log

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/src/auth.tsx

@@ -9,6 +9,7 @@ interface AuthCtx {
   login: (username: string, password: string) => Promise<void>;
   register: (username: string, password: string, displayName: string) => Promise<void>;
   logout: () => Promise<void>;
+  setUser: (u: User | null) => void;
 }
 
 const Ctx = createContext<AuthCtx | null>(null);
@@ -45,7 +46,7 @@ export function AuthProvider({ children }: { children: ReactNode }) {
     setUser(null);
   }, []);
 
-  return <Ctx.Provider value={{ user, loading, login, register, logout }}>{children}</Ctx.Provider>;
+  return <Ctx.Provider value={{ user, loading, login, register, logout, setUser }}>{children}</Ctx.Provider>;
 }
 
 export function useAuth(): AuthCtx {