Add session cookie support to WebSocket handshakes

[ryanfowler]

Summary

• Load named sessions for ws:// and wss:// requests, attach matching cookies to the upgrade request, and persist Set-Cookie headers from successful handshake responses.
• Reuse the existing HTTP session store by translating WebSocket URLs to their HTTP equivalents for cookie matching.
• Add an integration test covering HTTP login, WebSocket upgrade cookie transmission, and handshake cookie persistence.
• Update the repo notes to document the new WebSocket session behavior.

Testing

• cargo fmt
• cargo clippy --locked --all-targets --all-features -- -D warnings
• cargo test --all-features --test websocket -- --test-threads=1
• cargo test --all-features