yallm-config 0.1.0

Layered configuration loading for yallm.

Priority (high to low), each layer overwrites lower layers:

1. .yallm/secrets.toml - project secrets (gitignored)
2. .yallm/*.local.toml - per-machine overrides (gitignored)
3. .yallm/config.toml - project config (committed)
4. ~/.yallm/config.toml - user defaults
5. OS env vars
6. .env file (only fills keys absent from OS env)

Config files can have an [env] section. Values are returned in a merged map instead of being written back into the process environment.