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/package.json

@@ -1,17 +1,17 @@
 {
-  "name": "hashline-edit-benchmark",
+  "name": "hashline-edit-tests",
   "version": "0.1.0",
   "private": true,
   "type": "module",
-  "description": "Hashline edit tool benchmark using Vercel AI SDK with FriendliAI provider",
+  "description": "Hashline edit tool integration tests using Vercel AI SDK",
   "scripts": {
-    "bench:basic": "bun run test-edit-ops.ts",
-    "bench:edge": "bun run test-edge-cases.ts",
-    "bench:multi": "bun run test-multi-model.ts",
-    "bench:all": "bun run bench:basic && bun run bench:edge"
+    "test:basic": "bun run test-edit-ops.ts",
+    "test:edge": "bun run test-edge-cases.ts",
+    "test:multi": "bun run test-multi-model.ts",
+    "test:all": "bun run test:basic && bun run test:edge"
   },
   "dependencies": {
-    "@friendliai/ai-provider": "^1.0.9",
+    "@ai-sdk/openai-compatible": "^2.0.35",
     "ai": "^6.0.94",
     "zod": "^4.1.0"
   }