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.

src/chat/modelConfig.ts

@@ -10,7 +10,7 @@ export type AgentModelOption = {
 
 export const defaultAgentModelOptions: AgentModelOption[] = [
   {
-    id: "deepseek/deepseek-v4-flash",
+    id: "deepseek/deepseek-flash",
     label: "快速",
     description: "快速回答和任务执行",
     icon: "bolt",