Add searchable and flattened export, history re-export and diagnostics self-test

issueAndArchive keeps an issued invoice even when rendering or archiving
fails (Issued - not archived, with a Render & archive action). The export
menu offers a searchable PDF or a 300 DPI image-only PDF whose metadata is
the invoice number alone; flatten failures offer Retry or searchable export
and never silently lower the resolution. History re-exports the original
as issued by default and warns when a re-render's layout fingerprint
differs. The render client gains a FIFO assemble lane that previews cannot
supersede. A Diagnostics panel runs fixtures in the real worker and
compares against goldens generated from Node.

src/lib/exportDeps.ts

@@ -0,0 +1,25 @@
+import { save } from "@tauri-apps/plugin-dialog";
+import { api } from "./api";
+import { flattenInBrowser } from "./browserFlatten";
+import type { ExportDeps } from "./exportFlow";
+import { renderInvoicePdf } from "./pdf";
+import { getRenderClient, nextRenderJobId } from "./renderClient";
+import type { BankAccount, Settings } from "./types";
+
+/** The real collaborators of the export flow: Tauri commands, the render client, pdf.js and the save dialog. */
+export function createExportDeps(ctx: { settings: Settings; bank: BankAccount | null }): ExportDeps {
+  return {
+    issueInvoice: (input, renderPrefs) => api.issueInvoice(input, renderPrefs),
+    render: async (invoice) => {
+      const { bytes, fingerprint } = await renderInvoicePdf(invoice, ctx.settings, ctx.bank);
+      return { bytes, fingerprint };
+    },
+    archivePdf: api.archivePdf,
+    readArchive: api.readArchive,
+    flatten: (bytes, opts) => flattenInBrowser(bytes, opts),
+    assemble: async (pages, title) => (await getRenderClient().assemble({ id: nextRenderJobId(), pages, title })).bytes,
+    getLastExportDir: api.getLastExportDir,
+    save: ({ defaultPath }) => save({ defaultPath, filters: [{ name: "PDF document", extensions: ["pdf"] }] }),
+    writeExportFile: api.writeExportFile,
+  };
+}