CE-WP-0006/0007: Capture view polish, workplans, and UX refinements

- Blob URL stability, scroll centre, strip-only visual guide
- Focus-gated linking, unlink clears overlay, field badge tooltips
- Capture layout (viewer centre), grey guide lines, Add field button
- Workplans CE-WP-0006 (done) and CE-WP-0007 (T01-T09 done, T10-T12 todo)
- Integration tests and viewer-url helpers

src/source/index.ts

@@ -16,3 +16,8 @@ export {
   ingestPdfFromFile,
   type IngestPdfFromFileOptions,
 } from "./pdf/upload";
+export {
+  isEphemeralBlobUri,
+  resolvePdfViewerUrl,
+  documentHasUploadedBytes,
+} from "./pdf/viewer-url";