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/admin/lib/queries/offers.ts

@@ -52,7 +52,9 @@ export interface Customer {
 
 export const offerCustomersOptions = () =>
   queryOptions({
-    queryKey: ["offer-customers"],
+    // Under the broad ["offers"] domain so offer-domain invalidations
+    // (customer CRUD, offer mutations) refresh the picker automatically.
+    queryKey: ["offers", "customers"],
     queryFn: () => jsonQuery<Customer[]>("/api/admin/customers"),
     staleTime: 2 * 60_000,
   });
@@ -70,6 +72,21 @@ export const scopeTemplatesOptions = () =>
     queryFn: () => jsonQuery<ScopeTemplate[]>("/api/admin/offers-templates"),
   });
 
+/** Offer list row (the shape returned by GET /api/admin/offers). */
+export interface Quotation {
+  id: number;
+  quotation_number: string;
+  project_code: string;
+  customer_name: string;
+  created_at: string;
+  valid_until: string;
+  currency: string;
+  total: number;
+  status: string;
+  order_id?: number;
+  order_status?: string;
+}
+
 export const offerListOptions = (filters: {
   search?: string;
   sort?: string;
@@ -92,7 +109,9 @@ export const offerListOptions = (filters: {
       if (filters.customer_id)
         params.set("customer_id", String(filters.customer_id));
       const qs = params.toString();
-      return paginatedJsonQuery(`/api/admin/offers${qs ? `?${qs}` : ""}`);
+      return paginatedJsonQuery<Quotation>(
+        `/api/admin/offers${qs ? `?${qs}` : ""}`,
+      );
     },
   });
 
@@ -162,6 +181,8 @@ export interface OfferDetailData {
   status: string;
   order: OfferOrderInfo | null;
   locked_by: OfferLockInfo | null;
+  /** Legal next statuses, computed server-side (same contract as issued orders). */
+  valid_transitions: string[];
 }
 
 export const offerDetailOptions = (id: string | undefined) =>