Parse keyproxy.toml (listen address, [auth] token_ref, and the mpk-<name>
ref map) using a deliberate TOML subset implemented with the standard
library only. The surface is strict: unknown keys, malformed refs, and
backend-specific misconfigurations (e.g. env refs setting key, file refs
missing key) fail loudly at startup. The bearer-token ref must resolve
through the file backend. Parse errors carry line numbers, never line
contents.
💘 Generated with Crush
Assisted-by: Crush:glm-5.2
