fix(plugins): read the mem0 CLI key and ignore unexpanded host placeholders

The Python plugin core and the opencode, pi and deepseek plugins now fall back to the key `mem0 init` saves in ~/.mem0/config.json, so a configured CLI is enough to authenticate. The Python core also stops using or caching a literal ${api_key} left behind when a host (Cursor) does not expand its plugin variables, which is what kept asking for auth after the key was set.

Fixes #7346

integrations/pi-agent-plugin/src/config/index.ts

@@ -1,6 +1,7 @@
 import * as fs from "node:fs";
 import * as os from "node:os";
 import * as path from "node:path";
+import { mem0CliApiKey } from "../../../agent-plugin-core/typescript/src/credentials.ts";
 import type { Mem0Config } from "../types.ts";
 
 const AGENT_ROOT = path.join(os.homedir(), ".pi", "agent");
@@ -36,6 +37,9 @@ export function loadConfig(): Mem0Config {
   if (process.env.MEM0_API_KEY) {
     config.apiKey = process.env.MEM0_API_KEY;
   }
+  if (!config.apiKey) {
+    config.apiKey = mem0CliApiKey(os.homedir());
+  }
   if (process.env.MEM0_USER_ID) {
     config.userId = process.env.MEM0_USER_ID;
   }