Extract adapter registry across CLI, server, and UI

Refactor monolithic heartbeat service, AgentConfigForm, and CLI
heartbeat-run into a proper adapter registry pattern. Each adapter
type (process, claude-local, codex-local, http) gets its own module
with server-side execution logic, CLI invocation, and UI config form.
Significantly reduces file sizes and enables adding new adapters
without touching core code.

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

ui/src/adapters/index.ts

@@ -0,0 +1,8 @@
+export { getUIAdapter } from "./registry";
+export { buildTranscript } from "./transcript";
+export type {
+  TranscriptEntry,
+  StdoutLineParser,
+  UIAdapterModule,
+  AdapterConfigFieldsProps,
+} from "./types";