feat(web-search-deepseek): resolve provider options from the settings section

The provider now takes a thunk rather than a value: it projects the
authoritative section per search, so a stored endpoint, model, or key
reference reaches the next call without re-registering the provider — which
would make the seam's provider selection observable as a flicker.

apiKey already carries role('secret'), so the section is safe to describe:
the literal never rides a response in any layer and a configuration surface
learns only that a key is set.

pnpm-lock.yaml

@@ -7324,6 +7324,9 @@ importers:
       '@deepseek-ai/dsh-session':
         specifier: workspace:^
         version: link:../../core/session
+      '@deepseek-ai/dsh-settings':
+        specifier: workspace:^
+        version: link:../../settings/settings
       '@deepseek-ai/dsh-web':
         specifier: workspace:^
         version: link:../web