fix: 修正 logo 中 N 和 G 字母造型

N 添加对角线笔画（█▄ █），G 添加内横杠（█ ▀█），
避免与 O 字母造型雷同。同步更新 ui.ts 中的硬编码 wordmark。

packages/opencode/specs/effect/instance-context.md

@@ -0,0 +1,13 @@
+# Instance Context
+
+Instance selection is now Effect-provided context.
+
+Use these APIs:
+
+- `InstanceRef` for the current project context.
+- `WorkspaceRef` for the current workspace id.
+- `InstanceState.context` / `InstanceState.directory` inside Effect services that require an instance.
+- `InstanceStore` at entry boundaries that need to load, reload, or dispose project contexts.
+- `EffectBridge` for native, plugin, or plain JavaScript callback boundaries that need to re-enter Effect with captured refs.
+
+Do not add new ambient instance globals. Promise and callback boundaries should either stay in Effect, use `EffectBridge`, or pass the required context explicitly.