feat(httpapi): bridge config update endpoint

[kitlangton]

Summary

• Bridge PATCH /config through the experimental HttpApi path.
• Keep legacy Hono behavior while letting HttpApi defer active-instance disposal through the existing post-response lifecycle hook.
• Add a real Hono-bridge test for config persistence and instance disposal.
• Add a concrete Hono deletion checklist to the HttpApi migration spec.

Tests

• bun typecheck from packages/opencode
• bun run test:ci test/server/httpapi-*.test.ts from packages/opencode
• ./packages/sdk/js/script/build.ts
• bun turbo typecheck