feat: Add accounting period selector for all views

- Add PeriodSelectorMini component for global period selection
- Add accountingPeriod store for shared period state
- Add calendar service/router/model for available periods API
- Update Dashboard, Invoices, Trial Balance, Bank/Cash Register views
  to respect selected period
- Fix Trial Balance navigation sync bug (period now syncs on mount)
- Update backend services to accept luna/an parameters

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

reports-app/backend/app/main.py

@@ -25,7 +25,7 @@ from auth.middleware import AuthenticationMiddleware
 # from auth.routes import create_auth_router  # Fixed inline
 
 # Import routere locale
-from app.routers import invoices, dashboard, treasury, companies, telegram, cache, trial_balance
+from app.routers import invoices, dashboard, treasury, companies, telegram, cache, trial_balance, calendar
 
 # Auth endpoints pentru test
 from fastapi import APIRouter, HTTPException
@@ -318,6 +318,7 @@ app.include_router(treasury.router, prefix="/api/treasury", tags=["treasury"])
 app.include_router(telegram.router, prefix="/api/telegram", tags=["telegram"])
 app.include_router(cache.router, prefix="/api", tags=["cache"])
 app.include_router(trial_balance.router, prefix="/api/trial-balance", tags=["trial-balance"])
+app.include_router(calendar.router, prefix="/api/calendar", tags=["calendar"])
 
 @app.get("/")
 async def root():