fix(sap): canonical realtime entry + preserve login next + ignore persisted prep mode

[Cheewye]

What changed

• Home route (/) redirects to /map?start=realtime (no forced mode=preparacion).
• Protected routes redirect unauthenticated users to /login?next=<path+search+hash>.
• After login, navigation returns to next (only if it starts with /), otherwise falls back to /map?start=realtime (prevents open redirect).
• Map mode selection now obeys URL precedence:
  • If mode exists in query and is valid -> uses it.
  • If mode is missing -> forces operativo and closes any mode sheet (no restore from persisted state).
  • If mode is invalid -> degrades to operativo, closes sheet, and cleans URL to canonical realtime.
  • Keeps prevision as a valid mode (project uses it).
• “Preparation loading…” is no longer sticky: auto-hides after ~4s.

Why

• Avoid surprising default state (Preparation) on canonical realtime entry.
• Preserve user intent through auth redirect.
• Improve security by blocking external/open redirects.
• Prevent sessions getting stuck in a persisted Preparation state.

Files changed (frontend only)

• frontend/src/App.tsx
• frontend/src/components/auth/ProtectedRoute.tsx
• frontend/src/pages/LoginPage.tsx
• frontend/src/components/maps/realtime/hooks/useMapMode.ts
• frontend/src/components/maps/realtime/ModeSheetsHost.tsx

Verification

• npm -C frontend run build ✅ PASS
• Manual expectations:
  • /map?start=realtime opens in Operational (no auto-Preparation)
  • /map?start=realtime&mode=preparacion enters Preparation; loading hint auto-hides
  • invalid mode cleans to canonical realtime and returns to Operational