fix: sync Python type stubs (.pyi) with actual bindings and fix doc bugs (#250)

## Bug 1: Python type stubs missing 5 fields/classes

The pdf_inspector.pyi file was out of sync with the actual Python
bindings exposed via #[pyo3(get)] in src/python.rs. This breaks
IDE autocompletion and type checking (PyCharm, VS Code/Pylance, mypy)
for all Python users.

Added:
- PdfResult.ocr_reasons_by_page (python.rs:35)
- PageOcrReasons class with page and 
easons fields (python.rs:67-86)
- RegionText.ocr_reason (python.rs:136)
- PageMarkdown.ocr_reason (python.rs:193)
- PagesExtractionResult.ocr_reasons_by_page (python.rs:226)

## Bug 2: PdfResult.pages_needing_ocr indexing undocumented

PdfResult.pages_needing_ocr is 1-indexed (per python.rs:30) but
neither the .pyi stubs nor docs/python.md annotated this, while the
same field on PdfClassification was annotated as 0-indexed. Users
mixing both APIs would get wrong page numbers.

## Bug 3: README.md duplicate bullet character

The Markdown features table listed * twice in bullet prefixes.
The first should be ullet (U+2022), matching the actual source code in
src/markdown/mod.rs:34 which uses: ullet, dash, sterisk, circle, illed-circle, open-circle.

## Bug 4: docs/python.md missing fields in type reference

The Types section was missing PageOcrReasons, RegionText class
definition, ocr_reason fields, and ocr_reasons_by_page fields.

## Evidence

Cross-referenced every #[pyo3(get)] attribute in src/python.rs
against the .pyi declarations and docs/python.md type reference.

pdf_inspector.pyi

@@ -10,6 +10,9 @@ class PdfResult:
     page_count: int
     processing_time_ms: int
     pages_needing_ocr: list[int]
+    """1-indexed page numbers that need OCR."""
+    ocr_reasons_by_page: list["PageOcrReasons"]
+    """Machine-readable OCR reasons by 1-indexed page."""
     title: Optional[str]
     confidence: float
     is_complex_layout: bool
@@ -17,6 +20,13 @@ class PdfResult:
     pages_with_columns: list[int]
     has_encoding_issues: bool
 
+class PageOcrReasons:
+    """OCR reasons for a single 1-indexed page."""
+    page: int
+    """1-indexed page number."""
+    reasons: list[str]
+    """Machine-readable OCR reason identifiers."""
+
 class PdfClassification:
     """Lightweight PDF classification result."""
     pdf_type: str
@@ -47,6 +57,8 @@ class RegionText:
     text: str
     needs_ocr: bool
     """True when the text should not be trusted."""
+    ocr_reason: Optional[str]
+    """Machine-readable OCR reason when the cause is known."""
 
 class PageRegionTexts:
     """Extracted text for one page's regions."""
@@ -62,6 +74,8 @@ class PageMarkdown:
     """Formatted markdown for this page (empty string when needs_ocr is True)."""
     needs_ocr: bool
     """True when text on this page is unreliable and OCR should be used instead."""
+    ocr_reason: Optional[str]
+    """Machine-readable OCR reason when the cause is known."""
 
 class PagesExtractionResult:
     """Per-page markdown output with document-wide layout classification."""
@@ -73,6 +87,8 @@ class PagesExtractionResult:
     """1-indexed pages where multi-column layout was detected."""
     pages_needing_ocr: list[int]
     """1-indexed pages that need OCR."""
+    ocr_reasons_by_page: list[PageOcrReasons]
+    """Machine-readable OCR reasons by 1-indexed page."""
     is_complex: bool
     """True if any page has tables or multi-column layout."""