Fix debugger start ignoring save property

[OmChillure]

Summary

When debugger::Start runs a build task (via the "build" field in debug.json), it was bypassing the task's "save" property and calling project.create_terminal_task() directly. This meant unsaved files were never saved before the build ran, even when "save": "all" was set unlike task: spawn which correctly saved first.

Changes:

• Extracted Workspace::save_for_task(workspace, strategy, cx) as a shared async helper in workspace/src/tasks.rs
• Refactored schedule_resolved_task to call this helper (no behavior change, removes inline duplication)
• Called the same helper in RunningState::resolve_scenario before create_terminal_task, so the debugger build path now respects the task's save strategy
• Added test_save_for_task_all, test_save_for_task_current, and test_save_for_task_none tests covering the extracted helper directly

Self-Review Checklist

• I've reviewed my own diff for quality, security, and reliability
• Unsafe blocks (if any) have justifying comments
• The content is consistent with the UI/UX checklist
• Tests cover the new/changed behavior
• Performance impact has been considered and is acceptable

Closes #53284

Video after fix

Screencast.from.2026-04-08.08-04-18.webm

Release Notes:

• Fixed debugger not saving files before running a build task when "save": "all" is set in the task definition