Decouple TerminalSession from LocalProcessTerminalView

[trsdn]

Problem

TerminalSession (model layer) holds a direct reference to LocalProcessTerminalView (AppKit/SwiftTerm view):

var terminalView: LocalProcessTerminalView?

This couples the model to the view layer, preventing isolated testing and future renderer swaps.

Proposed Solution

Introduce a TerminalProcess protocol that abstracts startProcess, send, shellPid. TerminalSession references the protocol, not the concrete type.

Impact

• Enables unit testing of session logic without SwiftTerm
• Clean separation of concerns
• Foundation for potential alternative renderers