## Why
`features.multi_agent_v2` can be represented as either a legacy boolean toggle
or a table with an `enabled` field and nested settings. Layering or editing
configs that mix these forms could replace one form with the other and discard
the enabled state or nested settings.
## What changed
- Normalize boolean toggles to the table's `enabled` field when merging config
layers, applying CLI overrides, and editing user or profile config.
- Preserve nested multi-agent settings when toggling the feature, while keeping
ordinary replacement semantics for unrelated paths.
- Attribute normalized `enabled` values to the layer that supplied the boolean
toggle so config write results report overrides correctly.
## Testing
Added coverage for layered config, CLI overrides, config edits, app-server
writes, and origin metadata using both root and profile feature paths.
GitOrigin-RevId: 38b248c949b9ea5d6340a73d754f91c1834ac486
2f19a57704