refactor(tests): rename benchmarks/ to tests/hashline/, remove FriendliAI dependency

- Move benchmarks/ → tests/hashline/
- Replace @friendliai/ai-provider with @ai-sdk/openai-compatible
- Remove all 'benchmark' naming (package name, scripts, env vars, session IDs)
- Fix import paths for new directory depth (../src → ../../src)
- Fix pre-existing syntax error in headless.ts (unclosed case block)
- Inject HASHLINE_EDIT_DESCRIPTION into test system prompt
- Scripts renamed: bench:* → test:*

tests/hashline/test-multi-model.ts

@@ -14,10 +14,7 @@ import { resolve } from "node:path";
 
 // ── Models ────────────────────────────────────────────────────
 const MODELS = [
-  { id: "MiniMaxAI/MiniMax-M2.5", short: "M2.5" },
-  // { id: "MiniMaxAI/MiniMax-M2.1", short: "M2.1" },  // masked: slow + timeout-prone
-  // { id: "zai-org/GLM-5", short: "GLM-5" },            // masked: API 503
-  { id: "zai-org/GLM-4.7", short: "GLM-4.7" },
+  { id: "minimax-m2.5-free", short: "M2.5-Free" },
 ];
 
 // ── CLI args ──────────────────────────────────────────────────