ci: install codex and opencode CLIs in cli-tests job

The 15-provider test expects `provider models codex` and
`provider models opencode` to succeed, which requires the
actual CLI binaries to be on PATH.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.github/workflows/ci.yml

@@ -163,6 +163,9 @@ jobs:
       - name: Install dependencies
         run: npm install
 
+      - name: Install agent CLIs for provider tests
+        run: npm install -g @openai/codex opencode-ai
+
       - name: Build highlight dependency
         run: npm run build --workspace=@getpaseo/highlight