`intel.enabled` is the documented opt-in for the intel subsystem
(see commands/gsd/intel.md and docs/CONFIGURATION.md), but it was
missing from VALID_CONFIG_KEYS in config.cjs, so the canonical
command failed:
$ gsd-tools config-set intel.enabled true
Error: Unknown config key: "intel.enabled"
Add the key to the whitelist, document it under a new "Intel Fields"
section in planning-config.md alongside the other namespaced fields,
and cover it with a config-set test.
Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>