feat(documents)!: unify offers and issued orders end to end

One coherent pass over the two sibling document models, driven by a 3-lens
1:1 scan (~60 divergences inventoried) + user decisions. Migration adds
issued_orders.locked_by/locked_at and the issued_order_sections table
(mirror of scope_sections; applied to dev + test DBs).

Issued orders gained (offers as reference implementation):
- rich-text SECTIONS with CZ/EN titles, rendered on their own PDF page in
  the PO template's red style (shared DocumentSectionSchema, one-transaction
  create/update incl. items - fixes a torn-write bug)
- edit LOCKING (lock/heartbeat/unlock routes, 423 + holder name, 30s TTL =
  3 missed 10s heartbeats; locked_by enrichment on detail)
- archived-PDF serving: GET /:id/file reads the NAS copy (new
  readIssuedByNumber sweep) with live-render fallback + re-archive; offers'
  /file got the same fallback (kills the 'ulozte nabidku' dead end)
- NAS cleanup on delete, in-tx po_number uniqueness (409), collision-advancing
  number previews (also invoice previews), PUT returns assigned po_number

Offers hardened (issued as reference):
- VALID_TRANSITIONS enforced (no more numberless 'ordered' offers; invalidate
  follows the table; order creation only from active offers) +
  valid_transitions on detail
- explicit 400 instead of silent edits outside draft/active (mirrored on
  issued: explicit 400 replaced silent drops)
- customer existence check + Number(null)->0 clear bug fixed; delete of a
  linked offer -> 409 instead of P2003 500; error-token convention; Zod caps
  DB-aligned (desc 500/unit 20/number 50/project_code 100, isoDateString
  dates, ints for positions); audit old/new values + koncept fallbacks;
  list id tiebreaks; stats include trimmed; NAS delete dedupe

Frontend unification (6 new shared modules):
- components/document/{DocumentItemsEditor,SectionsEditor,LockBanner}
- hooks/{useDocumentLock,useUnsavedChangesGuard,useDocumentPdf(+list variant)}
- OfferDetail 1940->1100 lines, IssuedOrderDetail 1400->980: headline-only
  document number (form field removed), one form layout/readonly convention,
  view-permission opens read-only everywhere (issued's editable-for-viewers
  hole closed), server-driven transition buttons, dirty guard + Enter submit
  on both, useApiMutation everywhere (new opt-in envelope mode), fixed
  infinite spinner on failed detail fetch, draft PDFs hidden (no number yet)
- lists: supplier filter + count line on issued, Mena column dropped + mono
  numbers on offers, shared hardened per-row PDF flow (spinner, double-click
  guard, 401 close, blob cleanup), proper Czech quotes, real CTA empty
  states, query-lib cleanups (["offers","customers"] key, typed list rows,
  shared CurrencyAmount, retry:false on details)
- pdf-shared.ts: one escapeHtml/cleanQuillHtml(strict)/formatNum(NBSP)/
  formatCurrency/formatDate for all four PDF routes; offer PDF keeps its
  monochrome look (fractional qty fix: 1.5 no longer prints as 2); issued
  PDF language now comes from the document column

+49 tests (suite 364 -> 413). Each stage passed an independent review; final
cross-stage integration review verified the FE<->BE contracts.

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

src/services/numbering.service.ts

@@ -228,18 +228,30 @@ async function isInvoiceNumberTaken(number: string): Promise<boolean> {
   return !!existing;
 }
 
-/** Verify an issued-order (PO) number is not already used. */
-async function isIssuedOrderNumberTaken(number: string): Promise<boolean> {
-  const existing = await prisma.issued_orders.findFirst({
+/** Verify an issued-order (PO) number is not already used. Pass the tx client
+ *  when the check must be part of a transaction (otherwise it runs on a
+ *  separate connection and is only a best-effort pre-check). */
+export async function isIssuedOrderNumberTaken(
+  number: string,
+  client: Prisma.TransactionClient | PrismaClient = prisma,
+): Promise<boolean> {
+  const existing = await client.issued_orders.findFirst({
     where: { po_number: number },
+    select: { id: true },
   });
   return !!existing;
 }
 
-/** Verify an offer/quotation number is not already used. */
-export async function isOfferNumberTaken(number: string): Promise<boolean> {
-  const existing = await prisma.quotations.findFirst({
+/** Verify an offer/quotation number is not already used. Pass the tx client
+ *  when the check must be part of a transaction (otherwise it runs on a
+ *  separate connection and is only a best-effort pre-check). */
+export async function isOfferNumberTaken(
+  number: string,
+  client: Prisma.TransactionClient | PrismaClient = prisma,
+): Promise<boolean> {
+  const existing = await client.quotations.findFirst({
     where: { quotation_number: number },
+    select: { id: true },
   });
   return !!existing;
 }
@@ -440,7 +452,18 @@ export async function previewInvoiceNumber(
   const code = settings?.invoice_type_code || "81";
   const year = _year || new Date().getFullYear();
 
-  const seq = await previewNextSequence("invoice", year);
+  // Mirror generateInvoiceNumber's collision check (without consuming the
+  // sequence). The number_sequences counter can lag behind real data, so the
+  // raw next sequence may already be taken — advance past any number already
+  // used by an invoice so the preview matches what generateInvoiceNumber
+  // would actually assign instead of showing a stale, already-used number.
+  let seq = await previewNextSequence("invoice", year);
+  for (let attempt = 0; attempt < 1000; attempt++) {
+    const number = applyPattern(pattern, { year, prefix: "", code, seq });
+    if (!(await isInvoiceNumberTaken(number)))
+      return { number, next_number: number };
+    seq++;
+  }
   const number = applyPattern(pattern, { year, prefix: "", code, seq });
   return { number, next_number: number };
 }
@@ -482,7 +505,18 @@ export async function previewIssuedOrderNumber(
   const code = settings?.issued_order_type_code || "72";
   const year = _year || new Date().getFullYear();
 
-  const seq = await previewNextSequence("issued_order", year);
+  // Mirror generateIssuedOrderNumber's collision check (without consuming the
+  // sequence). The number_sequences counter can lag behind real data, so the
+  // raw next sequence may already be taken — advance past any number already
+  // used by an issued order so the preview matches what
+  // generateIssuedOrderNumber would actually assign.
+  let seq = await previewNextSequence("issued_order", year);
+  for (let attempt = 0; attempt < 1000; attempt++) {
+    const number = applyPattern(pattern, { year, prefix: "", code, seq });
+    if (!(await isIssuedOrderNumberTaken(number)))
+      return { number, next_number: number };
+    seq++;
+  }
   const number = applyPattern(pattern, { year, prefix: "", code, seq });
   return { number, next_number: number };
 }