docs: fix provider checklist, MCP anchors, and missing commands/settings (#11338)

Fix docs and `--help` drift: update the provider checklist to the
`src/api` layout, fix broken MCP anchors, and document `/mcp`, `pi mcp
add|remove`, `PI_CLEAR_ON_SHRINK`, and `"disabled"` timeouts.

closes #11243

packages/ai/README.md

@@ -1940,7 +1940,7 @@ Add a lazy wrapper `src/api/<api-id>.lazy.ts` (`<name>Api()` via `lazyApi()`) so
 - `createProvider()` wiring catalog + auth + the lazy API wrapper
 - Auth: `envApiKeyAuth` for standard key providers, a custom `ApiKeyAuth` for ambient auth (AWS profiles, ADC), `lazyOAuth` where an OAuth flow exists
 - Register the factory in `src/providers/all.ts`
-- If it is a new API: register it in the builtin list in `src/compat.ts` and add the package subpath export in `package.json`
+- If it is a new API: register it in the builtin list in `src/compat.ts`; the `./api/*` subpath export in `package.json` already covers the new module
 
 #### 5. Tests (`test/`)
 
@@ -1951,7 +1951,6 @@ Create or update test files to cover the new provider:
 - `abort.test.ts` - Request cancellation
 - `empty.test.ts` - Empty message handling
 - `context-overflow.test.ts` - Context limit errors
-- `image-limits.test.ts` - Image support (if applicable)
 - `unicode-surrogate.test.ts` - Unicode handling
 - `tool-call-without-result.test.ts` - Orphaned tool calls
 - `image-tool-result.test.ts` - Images in tool results
@@ -1967,15 +1966,15 @@ For providers with non-standard auth (AWS, Google Vertex), create a utility like
 
 Update `src/core/model-resolver.ts`:
 
-- Add a default model ID for the provider in `DEFAULT_MODELS`
+- Add a default model ID for the provider in `defaultModelPerProvider`
 
 Update `src/cli/args.ts`:
 
 - Add environment variable documentation in the help text
 
-Update `README.md`:
+Update `docs/providers.md`:
 
-- Add the provider to the providers section with setup instructions
+- Add setup instructions, the environment variable, and the `auth.json` key
 
 #### 7. Documentation