fix(invoice-inbox): switch from pdfjs-dist to unpdf (#409)

* fix(invoice-inbox): switch from pdfjs-dist to unpdf for PDF text extraction

After three rounds of fighting pdfjs on Vercel (#407 stubbed DOM globals,
#408 tried to ship the worker file via outputFileTracingIncludes), text
extraction still failed in prod with "Setting up fake worker failed" —
Next's tracer can't reliably include pdfjs-dist's worker file when the
package is marked as a server external.

unpdf is a serverless-first wrapper around pdfjs (by unjs) that ships its
own bundled pdfjs build with no canvas/worker dependencies. Drop-in
replacement: extractText returns merged page text directly.

- Remove DOM stubs, serverExternalPackages, outputFileTracingIncludes
- Replace pdfjs-dist with unpdf (no transitive deps)
- Update test mock from getDocument → extractText

All 45 invoice-inbox unit tests pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* fix(invoice-inbox): make unpdf import static, rename pdfjs test labels

Per Greptile review on #409:

1. CRITICAL: tryExtractPdfText was still using await import('unpdf'), a
   dynamic import. CLAUDE.md forbids dynamic imports in extensions
   precisely because Next.js bundling can't reliably trace them — which
   is the same class of failure that caused the pdfjs prod bug. unpdf
   bundles statically (no canvas/worker), so a top-level static import
   is safe and correct.

2. NIT: two test descriptions still said "pdfjs" after the mock rename.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

package.json

@@ -45,7 +45,6 @@
     "lucide-react": "^0.563.0",
     "next": "16.1.5",
     "next-themes": "^0.4.6",
-    "pdfjs-dist": "^5.4.530",
     "qrcode": "^1.5.4",
     "react": "19.2.3",
     "react-dom": "19.2.3",
@@ -57,6 +56,7 @@
     "sharp": "^0.34.5",
     "svix": "^1.85.0",
     "tailwind-merge": "^3.4.0",
+    "unpdf": "^1.6.2",
     "web-push": "^3.6.7",
     "xlsx": "^0.18.5",
     "zod": "^4.3.6"