Graft an existing working tree onto a remote git history

Wire up an existing on-disk working tree as a clone of a remote repo without losing local files. Use when: (1) a project's source files already exist on disk in directory X but X is not a git repo and the canonical repo lives at a remote URL, (2) the parent of X is a misconfigured git repo (only a stub README committed, with X and other unrelated dirs showing as untracked), (3) you cloned files manually or unpacked a tarball and now want to start tracking against the upstream remote, (4) you must preserve the local files exactly as they are (do not overwrite, do not stash) while still inheriting the remote's commit history. Covers the `git reset --mixed` vs `--soft` disti…