feat: support Agent Window sizing (session start --width/--height, window resize) (#52)

- `bsk session start --width <px> --height <px>` opens the Agent Window
  with the given outer size (chrome.windows.create)
- new `bsk window resize --session <id> --width <px> --height <px>`
  resizes the Agent Window at runtime (chrome.windows.update)
- both validated on CLI, daemon and extension sides (100..=7680 CSS px)
- protocol: new tool.window_resize method (BrowserMutation) and
  optional width/height on tool.session_start params; schemas regenerated

crates/bsk-protocol/src/tools/mod.rs

@@ -12,6 +12,7 @@ pub mod script;
 pub mod session;
 pub mod tabs;
 pub mod waits;
+pub mod window;
 
 pub use console::*;
 pub use dialog::*;
@@ -25,3 +26,4 @@ pub use script::*;
 pub use session::*;
 pub use tabs::*;
 pub use waits::*;
+pub use window::*;