docs(config): align environment and credential contracts

Code already treats $DSH_HOME/.env as ordinary launch environment and stores managed credentials in .credentials.yaml, but public docs still described the old store, old precedence, removed literal adapter keys, and the deleted TUI. That directed users to the wrong file and overstated the supported configuration surface.

Update the existing English and Chinese owners in place, document inherited > managed > project > user credential resolution, and record the loadLayeredEnv export. Regenerate only pairing records and the source-line catalog; add no new section or site route.

docs/user/guide/providers.md

@@ -31,7 +31,7 @@ That holds for providers that authenticate with an API key. The catalog also car
 
 **Let the endpoint report its models.** Expand **Model catalog** and choose **Fetch available models**: the interrogation asks the endpoint **the form currently shows** — including a base URL edited but not yet saved and a key typed but not yet stored — and offers what it reports as candidates to pick from. A route the installed catalog describes is answered from that catalog with no network call. Adopting a candidate only writes rows into the draft; nothing is stored until you save.
 
-Keys are write-only: the page only ever holds a redacted descriptor, never the literal secret. A key you enter is stored in `$DSH_HOME/.env`, and the profile records only the variable name that references it.
+Keys are write-only: the page only ever holds a redacted descriptor, never the literal secret. A key you enter is stored in `$DSH_HOME/.credentials.yaml`, and the profile records only the variable name that references it.
 
 ## settings.yaml for advanced configuration
 
@@ -89,9 +89,9 @@ Model ids are not lifecycle configuration. Requesting a model the route does not
 
 ## Credentials
 
-Prefer `apiKeyEnv`: it is a *reference* resolved per request, so no secret enters the configuration file. A literal `apiKey` is the escape hatch. Omitting both is what leaves a route unauthenticated, which for a catalog route means pi-ai's own environment discovery. A reference that resolves to nothing fails the request with `MISSING_CREDENTIAL` rather than falling through to whatever unrelated key the environment happens to hold.
+Use `apiKeyEnv`: it is a *reference* resolved per request, so no secret enters the configuration file. Omitting it leaves a route unauthenticated, which for a catalog route means pi-ai's own environment discovery. A reference that resolves to nothing fails the request with `MISSING_CREDENTIAL` rather than falling through to whatever unrelated key the environment happens to hold.
 
-References resolve from `$DSH_HOME/.env` — what the Models page's key fields write — and from the matching environment variable when no credential service is mounted. One credential serves every model on its route.
+Under `dsh`, references resolve from the inherited environment, the Models page's `$DSH_HOME/.credentials.yaml` store, the invoking directory's `.env`, then `$DSH_HOME/.env`. Without a credential service, a reference reads only the matching environment variable. One credential serves every model on its route.
 
 ## Point an agent at the new provider