Worktree-backend README section: delete or implement

[blooop]

Question

README.md:1468-1483 documents --shared and --warm with worked examples; both exit 2 in the shipped binary, and aid's source uses --shared as its canonical example of a flag dl does not know (rust/aid/src/rewrite.rs:576-582). The same section says worktrees where the implementation uses hardlinked clones, and docs/worktree-backend-spec.md documents --backend/DEVLAUNCH_BACKEND, never built, beside stale NOT-IMPLEMENTED checklists.

Decide: delete/mark-historical the section and spec, or ticket the features as real work. Specify the resulting build.

[blooop]

human-decided: Delete, as asked and as answered.

The README section's --shared/--warm worked examples document flags that have never existed in the Rust dl — clap exits 2, and aid's own test suite uses --shared as its canonical example of a flag dl does not know (rust/aid/src/rewrite.rs:601-608). The section's "git worktrees" claim contradicts workspace_clone.rs, which cuts hardlinked clones from a bare cache (repos_dir/owner/repo/.bare/ plus sibling clones). The accurate "What you get when you push and immediately launch" subsection survives under a truthful heading. docs/worktree-backend-spec.md goes too (or is banner-marked historical): its directory layout (.worktrees/ under the repo) contradicts the shipped layout despite the header's currency claim — git history keeps it.

Implementing the features instead was offered and declined — new feature scope beyond this map's destination. Unblocks #307, which owns the precise edits and the README-vs---help guard.