Replace the HTML preview with a worker-rendered PDF preview

Rendering moves into a module Web Worker behind a latest-wins RenderClient
with a watchdog and a handshake-based main-thread fallback. The preview
shows the real PDF through pdf.js at 2x with zoom, page indicator, audit
issues popover and a focus modal. A4/Letter and margin controls are frozen
into each invoice at issue and can be saved as the default (migration M3).
react-pdf and pdf.js are lazy-loaded; the main chunk shrinks from 1.8 MB
to 0.5 MB. The HTML twin and its styles are removed.

src/pdf/templates/harness.ts

@@ -50,6 +50,7 @@ const baseVendor: Settings = {
   defaultHsnSac: "",
   signatoryName: "",
   signatoryDesignation: "",
+  renderPrefs: "",
 };
 
 export const FIXTURE_BANK: BankAccount = {
@@ -210,6 +211,7 @@ export function buildFixture(spec: FixtureSpec): BuiltFixture {
     cancelledAt: null,
     cancelReason: "",
     archivedPdfSha256: null,
+    renderPrefs: "",
     items,
     ...spec.invoice,
   };