kit v0.9.0 -- project-local-first tool management

Kit now discovers context via kit.toml in your project root. When found,
lockfile and mise config are scoped to that project. Global state is
never modified.

New:
- kit init: create project-local kit.toml (seeds from global config)
- kit.toml walk-up resolution (like Cargo.toml)
- .kit.lock next to kit.toml (committed for reproducibility)
- .mise.toml merge with kit:begin/kit:end markers
- kit status shows provenance (kit-managed vs user-managed tools)
- Conflict detection when user and kit tool versions differ
- Global mode writes to conf.d/kit.toml (additive, not destructive)
- One-time migration of old "Managed by kit" config.toml

Changed:
- kit init --registry: existing registry creation (was default, now requires flag)
- Global mise output moves from config.toml to conf.d/kit.toml