This is a long-term, large sweeping project; design review is required before land.

Align Hammerhead's TOML dialect with Reef's existing reef.toml / packaging story so we do not invent a second dialect. Lang should weigh in on the design review when scheduled.

The work will likely need a TOML C library usable from Illumos-shaped userland (including login defaults and related consumers).

Related context: current /etc/default/login keys include RETRIES, SLEEPTIME, and DISABLETIME, and zyginit TOML is already used for console-login services. This issue is about broader /etc/default standardization, not redoing zyginit's existing TOML.

Owners: Ziggy (HH), with design review by Manny; Lang on dialect alignment; Oz as needed for the C library / OS integration.