This PR fixes an issue where session-scoped CDP settings configured at browser launch were not being re-applied to new CDP sessions/contexts, causing silent failures when users expected consistent behavior.

## Problem
Settings like `--user-agent`, `--color-scheme`, `--ignore-https-errors`, and download behavior were applied during initial browser launch but not propagated to new contexts created by `record start`, `tab new`, or `window new` operations. This meant recordings and new tabs would silently lose these configured behaviors.

## Changes
- **Centralized settings application**: Created `BrowserManager::apply_session_settings()` method that applies all session-scoped CDP commands in one place
- **Extended state storage**: Added `user_agent` and `color_scheme` fields to `BrowserManager` to persist launch-time configuration
- **Consistent application**: Updated all session creation code paths to call `apply_session_settings()` after attaching to new sessions
- **Eliminated duplication**: Replaced inline CDP calls in `launch()` and `handle_recording_start()` with centralized method

## Implementation Details
The new `apply_session_settings()` method handles the context-specific requirements of different CDP commands (e.g., `Browser.setDownloadBehavior` requires `browserContextId` parameter) and ensures all current and future session-scoped settings are automatically applied to every new session.

Fixes #1180