feat(bin): add gs script

[barbatdev]

Refs #63

Type

• New feature

Problem

The gs fish alias for git status was removed in a prior commit specifically to free the name for gentle-shell tooling, but the gs launcher script itself was never added to this repo, so it cannot be installed from a clean checkout.

Solution

• Add bin/gs verbatim (byte-for-byte copy of the working script), unchanged.
• Document it in the README's command table and directory structure.
• Document the one-time manual symlink step to ~/.local/bin/gs, since install.sh does not manage a bin/ directory of standalone scripts and no such mechanism exists yet in this repo. Adding a full installer for bin/ is left out of scope for this small change.

Changes

File	Change
bin/gs	New file: gentle-shell launcher + per-PR disposable worktree helper.
README.md	Documents bin/gs in the structure tree, command table, and the manual symlink step.

Manual step for the user

install.sh does not symlink bin/gs automatically. After pulling this change:

ln -sfn "$(pwd)/bin/gs" ~/.local/bin/gs

Validation

• bash -n bin/gs
• shellcheck --severity=error --shell=bash bin/gs (0 findings)
• bash -n install.sh
• HOME=$(mktemp -d) bash install.sh --check (0 FAIL, pre-existing warning count unaffected by this change)
• Two files changed, 333 lines added, well under the 400-line review budget.

Out of scope

• Building an automated installer/symlink mechanism for bin/.
• Changes to gs itself (copied verbatim).

Checklist

• Linked approved issue (Add gs script for gentle-shell + per-PR worktrees #63).
• Conventional commit, isolated work unit.
• Documentation included with the behavior.
• No credentials, personal paths, or private metadata.
• No automated attribution or Co-Authored-By trailers.