Carries two edits beyond conflict resolution, both forced by what master
brought in:
- `CustomProviderCard`: master added front-end key validation and a
component-level `keyValue` (already trimmed) while still writing
`apiKeyEnv` unconditionally. Kept this branch's blank-key rule and its
committed-profile retry gate, and adopted master's single `keyValue` so
the component has one spelling of the key rather than two.
- `docs/user/guide/providers`: master merged #1810, whose default-model
section still taught overriding the `api-gateway` row in
`$DSH_HOME/config.yaml` — the behavior this branch replaced. Rewritten
for the settings section the picker now writes, plus the review fix from
#1810 replacing the colloquial 挂着 in the opener.
d03d3ab70b