* feat: add -w/--worktree CLI flag to start in an isolated worktree
Enables `gsd -w` to auto-create a randomly-named worktree (adjective-verbing-noun
pattern) and `gsd -w my-feature` for named worktrees. Reuses existing worktree
infrastructure under .gsd/worktrees/ with worktree/<name> branches.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
* feat: full worktree lifecycle — subcommands, auto-commit on exit, status banners
Major improvements to the -w/--worktree system:
- `gsd worktree list` — show worktrees with status (files changed, commits, dirty)
- `gsd worktree merge [name]` — squash-merge into main and clean up
- `gsd worktree clean` — remove all merged/empty worktrees
- `gsd worktree remove <name>` — remove with --force safety gate
- `gsd -w` (no name) resumes the only active worktree instead of creating a new one
- `gsd -w` with multiple active worktrees shows a picker
- Auto-commit dirty work on session exit (session_shutdown hook)
- Status banner on normal `gsd` launch when unmerged worktrees exist
- Full help text with lifecycle documentation (`gsd worktree --help`)
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
