Service manager step 5: TOML parsing and service config

Summary

Add TOML config parsing to init for reading service definitions from /config/services/{name}/config.toml. Each config specifies the service binary, dependencies, restart policy, and optional protocol.

This is step 5 of the service manager implementation (#26).

Desired behaviour

• Add the toml crate (v0.9, no_std compatible) to init
• Parse ServiceConfig from TOML files at /config/services/{name}/config.toml
• Config fields:
  • binary: path to the service executable
  • args: optional command-line arguments
  • dependencies: list of service names this service depends on
  • restart: restart policy (always, on-failure, never)
  • protocol: optional protocol name for protocol-based service discovery
  • stop_timeout: grace period before SIGKILL after SIGTERM (default: 5s)

Example config

[service]
binary = "/initrd/terminal"
dependencies = ["keyboard"]
restart = "always"
protocol = "console"
stop_timeout = 5

Key files

• userspace/init/Cargo.toml — add toml dependency
• userspace/init/src/ — ServiceConfig struct and parser
• Config files in rootfs/config/services/ or embedded in initrd

Testing

• Unit tests for config parsing (valid configs, missing fields, invalid values)
• Test that all example configs parse correctly
• Test error reporting for malformed TOML

Documentation

• Document the config format with all supported fields
• Provide example configs for each built-in service
• Document the config search path and loading order

Part of #26

Start with userspace/init/Cargo.toml and inspect userspace/init/src/ for the existing ServiceConfig or service-manager entry points. Review the config files in rootfs/config/services/ and add unit coverage for valid, missing-field, invalid-value, and malformed TOML cases. Done means the documented fields and search path are supported and all example configs parse successfully.