feat(search): index PDF text, OCR scanned PDFs on import

Search now covers handwriting, the PDF text layer, AND scanned
(rasterized) PDFs.

- PdfTextIndexer runs at import: sums the embedded text layer across
  pages; if present it stores that as the document body, otherwise the
  PDF is rasterized and its rendered pages are OCR'd in the background.
  The result lands in the sidecar `pageText` field (distinct from
  `ocrText`, the handwriting OCR). Idempotent (skips a sidecar that
  already has pageText); degrades gracefully with no OCR engine.
- pdfrx_page_text_source abstracts text/render so it's testable.
- VaultSearchIndex now harvests title + typed text + handwriting OCR +
  PDF pageText, so search finds notes, typed PDFs and scanned PDFs.

analyze clean, 409 tests green.

test/badnote_sidecar_test.dart

@@ -379,6 +379,46 @@ void main() {
     expect(reparsed.background, isNull);
   });
 
+  test('pageText (PDF body / scanned-OCR text) round-trips through sidecar', () {
+    final original = BadnoteSidecar(
+      docType: 'pdf',
+      sourceFile: 'scan.pdf',
+      pageText: 'page one body\fpage two 第二页',
+    );
+    final reparsed = _roundTrip(original);
+    expect(reparsed.pageText, 'page one body\fpage two 第二页');
+    // ocrText (handwriting) and pageText (document body) are independent fields.
+    expect(reparsed.ocrText, isNull);
+    // Omitted when null/empty (no key bloat for legacy/annotation-only sidecars).
+    expect(BadnoteSidecar().toJson().containsKey('pageText'), isFalse);
+  });
+
+  test('missing pageText decodes to null (back-compat)', () {
+    // A sidecar authored before the import-OCR feature simply omits pageText.
+    final json = <String, dynamic>{
+      'badnoteSidecarVersion': 1,
+      'docType': 'pdf',
+      'sourceFile': 'old.pdf',
+      'strokes': <String, dynamic>{},
+      'highlights': <String, dynamic>{},
+      'bookmarks': <dynamic>[],
+      'scratchLinks': <dynamic>[],
+    };
+    final reparsed = BadnoteSidecar.fromJson(json);
+    expect(reparsed.pageText, isNull);
+  });
+
+  test('pageText and ocrText coexist independently', () {
+    final original = BadnoteSidecar(
+      docType: 'pdf',
+      ocrText: 'handwritten note',
+      pageText: 'printed document body',
+    );
+    final reparsed = _roundTrip(original);
+    expect(reparsed.ocrText, 'handwritten note');
+    expect(reparsed.pageText, 'printed document body');
+  });
+
   test('missing scratchpad defaults to 4000x4000 empty pad', () {
     final json = SidecarScratchLink(
       link: const ScratchLink(