fix(pdf): extract AcroForm field values, not just drawn page text

extractPdfText only read page.getTextContent(), which is content-stream
text - it never sees a filled-but-unflattened PDF form, since the values
live in annotation field data (fieldName/fieldValue), not on the page
itself. A PDF viewer that fills a form without flattening it (e.g. macOS
Preview) produces exactly this: pdftotext reads the field values, but
Mike's extractor returned the page as if it were blank, regardless of
which LLM read it downstream.

Now also read page.getAnnotations() per page and append any non-empty
field values as a `[Page N form fields]` block. Annotation reads are
wrapped in their own try/catch so one page's failure doesn't blank out
already-extracted text for the rest of the document.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>