feat: add model-aware DSH image input

DeepSeek Harness previously treated every selected model as text-only. It now carries the model profile's image capability through Main, the Utility Host, ACP, and Pi-AI, rejects unsupported images before model invocation, and validates supported JPEG/PNG data in a bounded process-local attachment store.

The Composer keeps universal controls on its first row, places OpenCode and Continue controls on a dedicated responsive row, and anchors context compaction without shifting the footer. Runtime supervision ownership for future Subagents and Jobs is documented for the right sidebar.

Release note: DeepSeek Harness 现可按所选模型连接的能力安全接收 JPEG/PNG 图片；Composer 同时将 Runtime 专属选择器移到独立一行，并固定上下文压缩入口。

src/main/agent/deepseek-harness-utility-launcher.test.ts

@@ -52,6 +52,7 @@ async function fixture() {
       signal: new AbortController().signal,
       baseUrl: 'https://gateway.example/openai/v1',
       model: 'qwen-plus',
+      supportsImageInput: false,
       credentialRefs: [DEEPSEEK_HARNESS_CREDENTIAL_REF],
       skillPackages: [],
       extensionPackages: []
@@ -103,6 +104,7 @@ describe('DeepSeek Harness utility launcher', () => {
       config: {
         baseUrl: 'https://gateway.example/openai/v1',
         model: 'qwen-plus',
+        supportsImageInput: false,
         credentialRefs: [DEEPSEEK_HARNESS_CREDENTIAL_REF]
       }
     })