feat(agent): migrate OpenCode 2 runtime and sandbox tools

Upgrade the runtime and native plugin API to OpenCode 2.0.24. Restore
session-scoped learning, credential renewal, typed project queries and
controlled frontend actions from the legacy Agent.

Replace host Shell execution with an approved Landlock/seccomp executor
and persistent per-session workspaces. Add typed Bocha search and Tianditu
geocoding bridges using the owning session credential. Require a working
kernel sandbox before startup and persist workspace files in deployments.

Validation completed before this commit: TypeScript checks, 150 Bun tests,
Docker build and UID 10001 sandbox execution, native Shell approval and
session recovery. Tianditu succeeded; Bocha currently reports exhausted
account quota. Unrelated investigation-report contract work is excluded.

.opencode/tools/final_answer.ts

@@ -0,0 +1,7 @@
+import { tool } from "../tool.js";
+
+export default tool({
+  description: "提交本轮完整的最终答复。只在全部工具结果、浏览器回执和业务写回已核实后调用；阶段说明留在过程记录。此工具不停止执行，也不代表任务、工单或运行已完成。",
+  args: { answer: tool.schema.string().min(1).max(30000) },
+  async execute({ answer }) { return JSON.stringify({ answer }); },
+});