refactor: merge duplicated helpers

[arzafran]

What this does

Merges copies of the same helper into one, with no behavior change. Copies that differ in timeout or output stay separate.

• App: the three identical shell single-quote helpers become one in GhosttyTerminalSupport.swift. The two Workspace initializers share their Bonsplit setup. TypingProfiler's run-loop label, the AgentTaskState mapping in telemetry, and the review error mapping each exist once.
• Swift tests: duplicate makeTemporaryDirectory, waitForCondition and git runners collapse into one each.
• tests_v2: 22 copies of _find_cli_binary and identical local wait helpers move into v2_support.py.

Review order

1. Sources/Workspace.swift (init extraction)
2. Sources/GhosttyTerminalSupport.swift, TerminalSurface.swift, CLIInstaller.swift (shell quoting)
3. tests_v2/v2_support.py, then the callers

Test plan

• CI passes (unit tests, tests_v2 subset, UI regressions)