Mouse selection, copy/paste, yield_to_user fixes

- Mouse text selection with highlight rendering in panes
- OSC 52 clipboard copy on selection, middle-click paste via tmux buffer
- Bracketed paste support (Event::Paste)
- yield_to_user: no tool result appended, ends turn immediately
- yield_to_user: no parameters, just a control signal
- Drop arboard dependency, use crossterm OSC 52 + tmux for clipboard

Co-Authored-By: Proof of Concept <poc@bcachefs.org>

Cargo.toml

@@ -20,6 +20,7 @@ edition.workspace = true
 
 [dependencies]
 anyhow = "1"
+crossterm = { version = "0.29", features = ["event-stream", "bracketed-paste", "osc52"] }
 clap = { version = "4", features = ["derive"] }
 figment = { version = "0.10", features = ["env"] }
 dirs = "6"
@@ -30,7 +31,6 @@ serde = { version = "1", features = ["derive"] }
 serde_json = "1"
 json5 = "1.3"
 
-crossterm = { version = "0.29", features = ["event-stream"] }
 ratatui = { version = "0.30", features = ["unstable-rendered-line-info"] }
 tui-markdown = { git = "https://github.com/koverstreet/tui-markdown", subdirectory = "tui-markdown" }
 tui-textarea = { version = "0.10.2", package = "tui-textarea-2" }