feat(llm-deepseek): per-request connection resolution over settings + credentials

The adapter takes an options thunk and a per-stream credential resolver
instead of frozen construction facts: base URL, catalog, defaults, idle
budget, and the API key re-resolve at each operation, so a settings or
credential change reaches the very next request while in-flight streams
keep the facts they started with. resolveAdapterOptions is the one explicit
resolve step (entry config fails loud at load; a live snapshot failing a
beyond-schema bound keeps the last good options). The plugin layers its
entry config under the optional llm-deepseek settings section and resolves
keys literal-first through ctx.credentials with an ambient env fallback; a
missing key now registers the route, warns, and fails each request with
actionable MISSING_CREDENTIAL instead of failing plugin load. The
registration-captured retry policy re-registers the route in place when it
changes.

pnpm-lock.yaml

@@ -2949,12 +2949,18 @@ importers:
         specifier: ^3.18.0
         version: 3.18.0
     devDependencies:
+      '@deepseek-ai/dsh-credentials':
+        specifier: workspace:^
+        version: link:../../credentials/credentials
       '@deepseek-ai/dsh-invariants':
         specifier: workspace:^
         version: link:../../support/invariants
       '@deepseek-ai/dsh-llm':
         specifier: workspace:^
         version: link:../llm
+      '@deepseek-ai/dsh-settings':
+        specifier: workspace:^
+        version: link:../../settings/settings
       '@deepseek-ai/dsh-timeout':
         specifier: workspace:^
         version: link:../../util/timeout