feat: add project onboarding detection and init wizard
Replace the silent .gsd/ bootstrap with an interactive init wizard that
detects project state, offers v1 migration, and guides users through
per-project configuration before their first milestone.
New commands:
- /gsd init — project init wizard (detect, configure, bootstrap .gsd/)
- /gsd setup — global setup status and routing to existing config commands
Detection engine (detection.ts):
- detectProjectState() identifies none/v1-planning/v2-gsd/v2-gsd-empty
- detectProjectSignals() scans for language, monorepo, CI, tests, package manager
- Auto-detects verification commands from package.json, Cargo.toml, go.mod, etc.
- isFirstEverLaunch() / hasGlobalSetup() for global state checks
Init wizard (init-wizard.ts):
- 8-step wizard: git → mode → verification → git prefs → instructions → advanced → bootstrap
- Every step skippable with sensible defaults
- offerMigration() when .planning/ detected (migrate/fresh/cancel)
- handleReinit() for safe re-init on existing projects
- Writes preferences.md from wizard answers + seeds CONTEXT.md with detected signals
Smart entry integration (guided-flow.ts):
- showSmartEntry() now runs detection before any bootstrap
- v1 .planning/ → migration offer before anything else
- No .gsd/ → init wizard instead of silent bootstrap
- Existing .gsd/ → unchanged behavior (zero regression)
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