feat: playground, CLI fingerprints, ACP support (#234, #223, #235)

- Add model playground page to dashboard (provider/model/endpoint selectors, Monaco editor, streaming, abort)
- Add CLI fingerprint matching (per-provider header/body ordering to match native CLI binaries)
- Add ACP module (CLI agent discovery, process spawner, session manager, API endpoint)
- Add playground to sidebar debug section with i18n support
- Close #192 and #200 as stale (v1.8.1, no repro info)

src/app/api/acp/agents/route.ts

@@ -0,0 +1,35 @@
+/**
+ * API Route: /api/acp/agents
+ *
+ * Returns the list of detected CLI agents and their availability status.
+ * Used by the dashboard to show ACP transport options.
+ */
+
+import { NextResponse } from "next/server";
+import { detectInstalledAgents } from "@/lib/acp";
+
+export const dynamic = "force-dynamic";
+
+export async function GET() {
+  try {
+    const agents = detectInstalledAgents();
+    return NextResponse.json({
+      agents: agents.map((a) => ({
+        id: a.id,
+        name: a.name,
+        binary: a.binary,
+        version: a.version,
+        installed: a.installed,
+        providerAlias: a.providerAlias,
+        protocol: a.protocol,
+      })),
+      available: agents.filter((a) => a.installed).length,
+      total: agents.length,
+    });
+  } catch (error: any) {
+    return NextResponse.json(
+      { error: error.message || "Failed to detect agents" },
+      { status: 500 }
+    );
+  }
+}