feat(HAI-071): add Bun single-binary compile support for CLI

- Create build script (packages/cli/build.ts) using Bun.build compile target
- Update asset resolution in dashboard server for bundled context
- Add npm scripts to wire up the build process
- Add build-exe tests to verify compiled binary output
- Fix pre-existing build errors in engine and core packages
- Document build and compile workflow in README

packages/cli/build.ts

@@ -0,0 +1,88 @@
+#!/usr/bin/env bun
+/**
+ * Bun compile build script for the `hai` CLI.
+ *
+ * Produces a single self-contained executable at packages/cli/dist/hai
+ * with the dashboard client assets co-located at packages/cli/dist/client/.
+ *
+ * Usage:
+ *   bun run build.ts
+ *
+ * Prerequisites:
+ *   - `pnpm build` must have been run first (dashboard client + tsc)
+ *   - Bun >= 1.0
+ */
+
+import { join, dirname } from "node:path";
+import { cpSync, mkdirSync, existsSync, rmSync } from "node:fs";
+
+const cliRoot = dirname(new URL(import.meta.url).pathname);
+const workspaceRoot = join(cliRoot, "..", "..");
+const outDir = join(cliRoot, "dist");
+const outBinary = join(outDir, process.platform === "win32" ? "hai.exe" : "hai");
+const dashboardClientSrc = join(workspaceRoot, "packages", "dashboard", "dist", "client");
+const dashboardClientDest = join(outDir, "client");
+
+// ── Validate prerequisites ────────────────────────────────────────────
+if (!existsSync(dashboardClientSrc)) {
+  console.error(
+    `ERROR: Dashboard client not built. Expected: ${dashboardClientSrc}\n` +
+    `Run 'pnpm build' first to build all packages.`,
+  );
+  process.exit(1);
+}
+
+// ── Clean previous output ─────────────────────────────────────────────
+if (existsSync(outBinary)) rmSync(outBinary);
+if (existsSync(dashboardClientDest)) rmSync(dashboardClientDest, { recursive: true });
+
+// ── Copy dashboard client assets alongside output ─────────────────────
+// Express.static requires a real filesystem directory, so we co-locate
+// the pre-built SPA next to the binary rather than embedding blobs.
+console.log("Copying dashboard client assets...");
+mkdirSync(dashboardClientDest, { recursive: true });
+cpSync(dashboardClientSrc, dashboardClientDest, { recursive: true });
+console.log(`  → ${dashboardClientDest}`);
+
+// ── Compile the CLI binary ────────────────────────────────────────────
+console.log("Compiling hai executable...");
+
+const entryPoint = join(cliRoot, "src", "bin.ts");
+
+const proc = Bun.spawnSync({
+  cmd: [
+    "bun", "build",
+    "--compile",
+    entryPoint,
+    "--outfile", outBinary,
+    "--target", "bun",
+    // Minify for smaller binary
+    "--minify",
+  ],
+  cwd: workspaceRoot,
+  stdout: "inherit",
+  stderr: "inherit",
+  env: {
+    ...process.env,
+    // Ensure workspace resolution works
+    NODE_PATH: join(workspaceRoot, "node_modules"),
+  },
+});
+
+if (proc.exitCode !== 0) {
+  console.error(`\nBun compile failed with exit code ${proc.exitCode}`);
+  process.exit(proc.exitCode ?? 1);
+}
+
+// ── Write a minimal package.json next to the binary ───────────────────
+// Some bundled dependencies (e.g. express) probe for package.json at
+// runtime. Provide a minimal one so the binary can self-resolve.
+import { writeFileSync } from "node:fs";
+writeFileSync(
+  join(outDir, "package.json"),
+  JSON.stringify({ name: "hai", version: "0.1.0", type: "module" }, null, 2) + "\n",
+);
+
+console.log(`\n✓ Built: ${outBinary}`);
+console.log(`  Assets: ${dashboardClientDest}`);
+console.log(`\nRun with: ${outBinary} --help`);