feat: add Python bindings via PyO3

Expose the pdf-inspector Rust library as a Python package using PyO3 + maturin.
Python users can now `pip install` and use `import pdf_inspector` for PDF
classification, text extraction, and markdown conversion with native Rust speed.

Adds:
- src/python.rs: PyO3 bindings (process_pdf, detect_pdf, extract_text, etc.)
- pyproject.toml: maturin build configuration
- pdf_inspector.pyi: type stubs for IDE support
- tests/test_python.py: 21 pytest tests covering all Python API functions
- examples/basic_usage.py: example script demonstrating all features
- Updated README with Python quick start and API reference

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

pdf_inspector.pyi

@@ -0,0 +1,56 @@
+"""Type stubs for pdf_inspector."""
+
+from typing import Optional
+
+class PdfResult:
+    """Result of processing a PDF file."""
+    pdf_type: str
+    """'text_based', 'scanned', 'image_based', or 'mixed'."""
+    markdown: Optional[str]
+    page_count: int
+    processing_time_ms: int
+    pages_needing_ocr: list[int]
+    title: Optional[str]
+    confidence: float
+    is_complex_layout: bool
+    pages_with_tables: list[int]
+    pages_with_columns: list[int]
+    has_encoding_issues: bool
+
+class TextItem:
+    """A positioned text item extracted from a PDF."""
+    text: str
+    x: float
+    y: float
+    width: float
+    height: float
+    font: str
+    font_size: float
+    page: int
+    is_bold: bool
+    is_italic: bool
+    item_type: str
+
+def process_pdf(path: str, pages: Optional[list[int]] = None) -> PdfResult:
+    """Process a PDF: detect type, extract text, convert to Markdown."""
+    ...
+
+def process_pdf_bytes(data: bytes, pages: Optional[list[int]] = None) -> PdfResult:
+    """Process a PDF from bytes in memory."""
+    ...
+
+def detect_pdf(path: str) -> PdfResult:
+    """Fast detection only — no text extraction."""
+    ...
+
+def detect_pdf_bytes(data: bytes) -> PdfResult:
+    """Fast detection from bytes."""
+    ...
+
+def extract_text(path: str) -> str:
+    """Extract plain text from a PDF."""
+    ...
+
+def extract_text_with_positions(path: str, pages: Optional[list[int]] = None) -> list[TextItem]:
+    """Extract text with position information."""
+    ...