feat(ui): add instructions file path field to adapter config forms

Add agent instructions file field to Claude and Codex adapter
config panels, allowing users to specify an absolute path to an
AGENTS.md-style file injected into the system prompt at runtime.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ui/src/components/agent-config-defaults.ts

@@ -3,6 +3,7 @@ import type { CreateConfigValues } from "@paperclip/adapter-utils";
 export const defaultCreateValues: CreateConfigValues = {
   adapterType: "claude_local",
   cwd: "",
+  instructionsFilePath: "",
   promptTemplate: "",
   model: "",
   thinkingEffort: "",