refactor(llm): recover IMAGE_OFFLOAD_REQUIRED in llm-retry instead of a new plugin package

Remove the llm-image-offload package and every registration it needed. The
recovery branch lives in dsh-llm-retry, which already sits on the
agent/request-error waterfall: an IMAGE_OFFLOAD_REQUIRED failure advances the
image/offload watermark by the count the adapter names and retries the step
outside the provider retry budget. Drop pre-dispatch planning with it: routes
no longer declare a request-image budget on their model info, and the byte
checks that stay in the DeepSeek and pi-ai adapters are provisional until the
provider reports uncacheable images itself.

python/sdk-runtime/package.json

@@ -53,7 +53,6 @@
     "@deepseek-ai/dsh-llm": "workspace:^",
     "@deepseek-ai/dsh-llm-deepseek": "workspace:^",
     "@deepseek-ai/dsh-llm-pi-ai": "workspace:^",
-    "@deepseek-ai/dsh-llm-image-offload": "workspace:^",
     "@deepseek-ai/dsh-llm-retry": "workspace:^",
     "@deepseek-ai/dsh-mcp-client": "workspace:^",
     "@deepseek-ai/dsh-output-retention": "workspace:^",