Persistent Config Store with Remote Get/Set

[rodneyosodo]

The Zephyr agent (Aeolus) has an NVS-backed persistent key-value store (src/config/config.c) that survives reboots. Runtime config changes are made via MQTT config set commands and persist immediately.

The Linux agent currently has no persistent config store — all configuration comes from environment variables and the bootstrap response at startup. There is no way to change settings at runtime.

What to implement:

• Local config file (e.g. JSON or TOML) that persists across restarts
• MQTT config get <key> — read a config value, respond on res topic
• MQTT config set <key> <value> — write a config value to persistent store
• On startup, merge: env vars → bootstrap response → persisted overrides

Reference: Aeolus config module — src/config/config.c, docs/config.md