feat(invoices)!: Obsah sections, internal-only notes, unified per-page PDF header+footer

Invoices now mirror the issued-orders document model:

- New invoice_sections table (CZ/EN rich-text "Obsah") edited via the
  shared SectionsEditor, printed inline right after the items on the
  PDF. Full-replace on update, same transaction as items.
- Printed notes dropped: the notes column is removed (migration merges
  existing content into internal_notes first); the form field is now
  "Interni poznamky", never printed. Legacy payloads sending notes are
  silently stripped.
- Form cleanup: Cislo faktury and Vystavil fields removed (number lives
  in the header, issued_by auto-fills); page header title restyled to
  the orders/offers pattern (number span + status chip).
- Unified per-page PDF header for the red-accent family: shared
  buildPdfHeaderTemplate in pdf-shared (22mm logo, red heading, red
  rule) rendered by a Puppeteer headerTemplate on EVERY page of both
  invoices and issued orders (incl. the /file fallback render); body
  headers are print-hidden. htmlToPdf gained the headerTemplate option.
- Footer parity: invoices get the per-page "Vystavil + Strana X z Y"
  footer; the invoice bottom block (notice + QR/VAT recap + Prevzal)
  is break-inside: avoid so a page break can never split it.
- @page margins now match the template space (32mm top, 18mm bottom) -
  Chromium lays out by CSS @page margins, which also fixes issued
  orders' content running into the 18mm footer zone on full pages.

BREAKING CHANGE: invoices.notes column dropped (data merged into
internal_notes); deploy must run prisma migrate deploy + generate.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/admin/lib/queries/invoices.ts

@@ -43,6 +43,14 @@ export interface InvoiceItem {
   position?: number;
 }
 
+export interface InvoiceSection {
+  id?: number;
+  title: string | null;
+  title_cz: string | null;
+  content: string | null;
+  position?: number | null;
+}
+
 export interface InvoiceDetail {
   id: number;
   invoice_number: string;
@@ -62,7 +70,7 @@ export interface InvoiceDetail {
   vat_rate: number;
   apply_vat: boolean;
   exchange_rate: string;
-  notes?: string;
+  internal_notes?: string | null;
   payment_method?: string;
   variable_symbol?: string;
   constant_symbol?: string;
@@ -75,6 +83,7 @@ export interface InvoiceDetail {
   bank_account?: string;
   bank_account_id?: number | null;
   items?: InvoiceItem[];
+  sections?: InvoiceSection[];
   subtotal: number;
   vat_amount: number;
   total: number;