Add streaming query support that yields real-time retrieval events as
dicts with type information. This includes a new StreamingQuery async
iterator that bridges Rust's mpsc::Receiver<RetrieveEvent> to Python.

- Introduce PyStreamingQuery wrapper for async iteration over events
- Add query_stream method to PyEngine with proper event conversion
- Bridge RetrieveEvent variants to Python dictionaries with "type" keys
- Provide proper terminal event handling (completed/error)
- Update Session.query_stream to use real Rust-side streaming
- Add StreamingQueryResult to consume and process streaming events

refactor(docs): update navbar styling and disable blog link

Replace hardcoded colors with CSS variables for theme consistency.
Apply subtle gradient background pattern to navbar. Clean up redundant
styles and remove dark mode specific overrides.

- Replace hardcoded hex colors with --text, --text-light variables
- Add grid-like gradient background pattern using linear gradients
- Remove duplicate border/box-shadow declarations
- Hide navbar pseudo-elements for cleaner appearance

feat(python): introduce SyncSession for synchronous operations

Provide synchronous Vectorless API that works in scripts and Jupyter
notebooks without requiring async/await syntax. Uses background event
loop management for compatibility across different environments.

- Create SyncSession wrapping Session with sync methods
- Implement run_async utility for event loop bridging
- Add synchronous versions of all core operations (index, ask, etc.)
- Support both new and existing event loop contexts

refactor(python): enhance LangChain and LlamaIndex compatibility

Update LangChain and LlamaIndex integrations to support passing
Session instances for engine reuse. Replace asyncio.run usage with
robust async-to-sync bridging utility.

- Add session parameter to VectorlessRetriever constructors
- Implement lazy session creation with caching
- Use run_async instead of asyncio.run for better compatibility
- Maintain backward compatibility with existing API patterns