feat(mcp): add MCP Server Card at /.well-known/mcp/server-card.json

Implements SEP-1649 server card so MCP clients can discover the server's
transport and capabilities without prior configuration.

Version is read dynamically from package.json. The endpoint advertises
the streamable-http transport mounted at /api/mcp.

Spec: modelcontextprotocol/modelcontextprotocol#2127

Author: nocoo

src/app/.well-known/mcp/server-card.json/route.test.ts

@@ -0,0 +1,48 @@
+import { describe, it, expect } from "vitest";
+
+import pkg from "../../../../../package.json";
+
+import { GET } from "./route";
+
+describe("GET /.well-known/mcp/server-card.json", () => {
+  it("returns 200 with JSON content type", async () => {
+    const response = GET();
+    expect(response.status).toBe(200);
+    expect(response.headers.get("Content-Type")).toBe("application/json");
+  });
+
+  it("sets Cache-Control header for 1 hour", () => {
+    const response = GET();
+    expect(response.headers.get("Cache-Control")).toBe(
+      "public, max-age=3600",
+    );
+  });
+
+  it("advertises serverInfo with name and dynamic package version", async () => {
+    const response = GET();
+    const body = await response.json();
+    expect(body.serverInfo).toEqual({
+      name: "firefly",
+      version: pkg.version,
+    });
+  });
+
+  it("advertises streamable-http transport pointing at /api/mcp", async () => {
+    const response = GET();
+    const body = await response.json();
+    expect(body.transport).toEqual({
+      type: "streamable-http",
+      endpoint: "/api/mcp",
+    });
+  });
+
+  it("advertises capabilities (tools + resources, no prompts)", async () => {
+    const response = GET();
+    const body = await response.json();
+    expect(body.capabilities).toEqual({
+      tools: true,
+      resources: true,
+      prompts: false,
+    });
+  });
+});

src/app/.well-known/mcp/server-card.json/route.ts

@@ -0,0 +1,35 @@
+import pkg from "../../../../../package.json";
+
+/**
+ * MCP Server Card endpoint (SEP-1649).
+ *
+ * Advertises this server's MCP capabilities and transport so that clients
+ * can discover the MCP endpoint without prior configuration.
+ *
+ * Spec: https://github.com/modelcontextprotocol/modelcontextprotocol/pull/2127
+ */
+export function GET() {
+  const body = {
+    serverInfo: {
+      name: "firefly",
+      version: pkg.version,
+    },
+    transport: {
+      type: "streamable-http",
+      endpoint: "/api/mcp",
+    },
+    capabilities: {
+      tools: true,
+      resources: true,
+      prompts: false,
+    },
+  };
+
+  return new Response(JSON.stringify(body), {
+    status: 200,
+    headers: {
+      "Content-Type": "application/json",
+      "Cache-Control": "public, max-age=3600",
+    },
+  });
+}