feat: doctor and adopt

AGENTS.md

@@ -24,12 +24,15 @@ not repeated here.
 - `internal/gitsync/`: fetches a set of repositories through a bounded pool of workers; never
   pulls, rebases or merges. Named apart from `sync` so no caller shadows the standard library
   package of that name.
+- `internal/doctor/`: detects identity drift, a repository at a path the layout would not
+  render, a missing or stale managed file and a global identity key. Detection only; the
+  command layer writes.
 - `internal/shell/`: the per shell init snippet `shell-init` prints.
 
-`list`, `cd`, `doctor` and `adopt` are later milestones, tracked as issues; their own packages
-land with them. `cmd/gitcd/discover.go` walks the configured root for `status`, `sync` and
-`open`; issue #3's `internal/scan` walks the same ground for `list`, `doctor` and `adopt` with
-a richer value, and the two should be reconciled into one once both have landed.
+`list` and `cd` are a later milestone, tracked as an issue; their own packages land with them.
+`cmd/gitcd/discover.go` walks the configured root for `status`, `sync`, `open` and `doctor`;
+issue #3's `internal/scan` walks the same ground for `list` and `cd` with a richer value, and
+issue #15 reconciles the two into one once both have landed.
 
 ## Commands