refactor: redesign public API for better usability

- Remove `process_mode` from `MarkdownOptions` (it controlled the
  pipeline, not markdown formatting)
- Remove dead `text` field from `PdfProcessResult`
- Add `PdfOptions` builder consolidating mode, detection, markdown,
  and page filter configuration
- Add convenience functions: `detect_pdf()`, `detect_pdf_mem()`,
  `process_pdf_with_options()`, `process_pdf_mem_with_options()`
- Eliminate double document parsing: load once, share between
  detection and extraction via internal `pub(crate)` helpers
- Deprecate old `process_pdf_with_config*` functions (kept as shims)
- Update binaries to use new API

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/extractor/mod.rs

@@ -134,8 +134,8 @@ pub(crate) fn extract_text_with_positions_mem_and_rects(
 // Orchestration
 // ---------------------------------------------------------------------------
 
-/// Extract positioned text and rectangles from loaded document
-fn extract_positioned_text_from_doc(
+/// Extract positioned text and rectangles from a pre-loaded document.
+pub(crate) fn extract_positioned_text_from_doc(
     doc: &Document,
     font_cmaps: &FontCMaps,
     page_filter: Option<&HashSet<u32>>,