Update constructor calls (6-arg), seed AppSettings with sibling strategy,
git-init working dirs via GitRepoFixture.InitRepoWithInitialCommit, and
replace McpConfigPath assertions with worktree-path / .mcp.json checks.
Also fixes PlanningHubTests which had the same 3-arg constructor.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>