feat: expose per-page markdown extraction to Python and Node (#53)

* feat: expose per-page markdown extraction to Python and Node (#49)

Implements the feature requested in issue #49: a list-of-pages markdown output
from the Python API. Matching the existing project pattern, the feature lives
in the Rust core and is surfaced through every binding.

- Rust core: `extract_pages_markdown` (path) and `extract_pages_markdown_mem`
  (bytes) now take `Option<&[u32]>` — `None` returns every page in document
  order; a slice restricts and preserves caller order.
- Python: new `extract_pages_markdown(path, pages=None)` and
  `extract_pages_markdown_bytes(data, pages=None)` functions plus
  `PageMarkdown` / `PagesExtractionResult` classes; stub file updated.
- Node: `extractPagesMarkdown(buffer, pages?)` — `pages` is now optional.
- Tests: 2 new Rust integration tests, 9 new Python tests, 2 new Node
  assertions. All 372 unit + 107 integration + 53 Python tests pass.

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

* chore: bump version from 1.3.0 to 1.4.0

Minor bump for the new per-page markdown extraction API exposed through
the Python and Node bindings.

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

---------

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

napi/test.mjs

@@ -7,6 +7,7 @@ import {
   extractText,
   extractTextWithPositions,
   extractTextInRegions,
+  extractPagesMarkdown,
 } from './index.js';
 
 const fixture = readFileSync('../tests/fixtures/thermo-freon12.pdf');
@@ -89,6 +90,28 @@ assert.equal(typeof regionResults[0].regions[0].text, 'string');
 assert.equal(typeof regionResults[0].regions[0].needsOcr, 'boolean');
 console.log('  extractTextInRegions: OK');
 
+// --- extractPagesMarkdown ---
+console.log('Testing extractPagesMarkdown...');
+
+// omit pages → every page in document order
+const allPages = extractPagesMarkdown(fixture);
+assert.equal(allPages.pages.length, 3);
+assert.deepEqual(allPages.pages.map(p => p.page), [0, 1, 2]);
+assert.ok(typeof allPages.pages[0].markdown === 'string');
+assert.equal(typeof allPages.pages[0].needsOcr, 'boolean');
+assert.ok(Array.isArray(allPages.pagesWithTables));
+assert.ok(Array.isArray(allPages.pagesWithColumns));
+assert.ok(Array.isArray(allPages.pagesNeedingOcr));
+assert.equal(typeof allPages.isComplex, 'boolean');
+console.log('  extractPagesMarkdown (no pages arg): OK');
+
+// selected pages preserve caller order
+const picked = extractPagesMarkdown(fixture, [2, 0]);
+assert.equal(picked.pages.length, 2);
+assert.equal(picked.pages[0].page, 2);
+assert.equal(picked.pages[1].page, 0);
+console.log('  extractPagesMarkdown with pages: OK');
+
 // --- Error handling ---
 console.log('Testing error handling...');
 assert.throws(() => processPdf(Buffer.from('not a pdf')), /process_pdf/);