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.

packages/llm/llm-deepseek/tsconfig.json

@@ -20,6 +20,12 @@
     {
       "path": "../../llm/llm"
     },
+    {
+      "path": "../../credentials/credentials"
+    },
+    {
+      "path": "../../settings/settings"
+    },
     {
       "path": "../../support/invariants"
     },