Dai Ha
f9073e2320
docs: CB-301-ext spec — worktree provisioning + config-parity overlay
Opt-in per-acquire worktree (shared-tree default preserved). git behind a
Worktrees seam (ProcessBuilder impl, fake in tests). acquire provisions
worktree+branch, overlays local config (copy + --skip-worktree on tracked
files so the worker can't commit .mcp.json), spawns with cwd=worktree.
release removes the worktree but keeps the branch (holds commits/PR).
WorkerSession gains nullable worktree/branch; BridgedConfig.Worker gains
parityOverlay. 6 fake-based acceptance tests incl. backward-compat + unwind.