feat: add OpenCode agent provider with DeepSeek support

- Copy opencode provider files from upstream/providers
- Add self-registration imports to host and container barrels
- Install @opencode-ai/sdk@1.4.17 in agent-runner
- Add opencode-ai@1.4.17 to container Dockerfile
- Configure .env template for DeepSeek

container/agent-runner/package.json

@@ -11,6 +11,7 @@
   "dependencies": {
     "@anthropic-ai/claude-agent-sdk": "^0.2.128",
     "@modelcontextprotocol/sdk": "^1.12.1",
+    "@opencode-ai/sdk": "1.4.17",
     "cron-parser": "^5.0.0",
     "zod": "^4.0.0"
   },