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>

server/src/adapters/http/index.ts

@@ -0,0 +1,8 @@
+import type { ServerAdapterModule } from "../types.js";
+import { execute } from "./execute.js";
+
+export const httpAdapter: ServerAdapterModule = {
+  type: "http",
+  execute,
+  models: [],
+};