fix(workspace): stage task files in the packet repository

[cookerpapa]

Wave preflight stages task files only in the default repository. When task packets live in another workspace repo, their paths are skipped and the orch branch never receives uncommitted PROMPT.md or STATUS.md files.

Thread workspace context into ensureTaskFilesCommitted and use the validated routing.taskPacketRepo as the staging repository. Keep the existing temporary-index commit flow and repo-mode behavior.

Fixes #479.

Validation:

• 33 targeted tests passed. New tests use real Git repositories and worktrees, verify wave-preflight routing, and check that HEAD and the user's index remain unchanged.
• Typecheck, lint, format, and diff checks passed.
• Standalone full suite: 4,101 passed, 6 existing path/template failures addressed by fix(runtime): honor agent prompt inheritance across roles #648 and fix(paths): handle Windows separators and absolute pointers on POSIX #649.
• Applied together with fix(runtime): honor agent prompt inheritance across roles #648 and fix(paths): handle Windows separators and absolute pointers on POSIX #649 without conflicts: all 4,123 tests passed.

This branch is based directly on main and contains only this fix.