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/utils/html-to-pdf.ts

@@ -74,6 +74,15 @@ export interface HtmlToPdfOptions {
    * Chromium's default date/title header.
    */
   footerTemplate?: string;
+  /**
+   * Chromium headerTemplate HTML rendered in the top margin of EVERY page
+   * (same rules as footerTemplate: inline styles, explicit font-size; images
+   * must be data: URLs). When set, the top margin grows to 32mm to make room
+   * — the document body must NOT render its own header then, or page 1 shows
+   * it twice. NOTE: Chromium lays pages out by the document's CSS @page
+   * margins when present (they override this option) — keep them in sync.
+   */
+  headerTemplate?: string;
 }
 
 export async function htmlToPdf(
@@ -95,16 +104,16 @@ export async function htmlToPdf(
       format: "A4",
       printBackground: true,
       margin: {
-        top: "10mm",
+        top: options.headerTemplate ? "32mm" : "10mm",
         bottom: options.footerTemplate ? "18mm" : "10mm",
         left: "10mm",
         right: "10mm",
       },
-      ...(options.footerTemplate
+      ...(options.footerTemplate || options.headerTemplate
         ? {
             displayHeaderFooter: true,
-            headerTemplate: "<span></span>",
-            footerTemplate: options.footerTemplate,
+            headerTemplate: options.headerTemplate || "<span></span>",
+            footerTemplate: options.footerTemplate || "<span></span>",
           }
         : {}),
       timeout: 15_000,