feat: UX improvements — nav, reports tabs, dashboard alerts, transaction hints, settings layout

- Move Reports to Finans nav group and auto-expand Övrigt on its pages
- Make report tabs horizontally scrollable with gradient fade on mobile
- Surface deadlines and alerts above the fold on dashboard
- Add dismissible categorization hint card on transactions page
- Split settings company form into 4 separate Cards for scannability
- Add monthly breakdown report, document upload zone, journal entry attachments
- Add batch category selector, receipt document linking, invoice form improvements

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

supabase/migrations/20240101000029_add_receipt_document_id.sql

@@ -0,0 +1,6 @@
+-- Add document_id to receipts for linking receipt images to WORM archive documents
+ALTER TABLE public.receipts
+  ADD COLUMN document_id uuid REFERENCES public.document_attachments(id) ON DELETE SET NULL;
+
+-- Index for efficient lookups
+CREATE INDEX idx_receipts_document_id ON public.receipts (document_id);