test: add e2e and LLM eval tests for SKILL.md setup block

- 3 Agent SDK e2e tests: happy path, NEEDS_SETUP, non-git-repo
- LLM eval: setup block clarity + actionability >= 4
- New error pattern: 'no such file or directory.*browse'

These tests catch the exact failure mode where agents can't discover
the browse binary via SKILL.md instructions.

test/helpers/session-runner.ts

@@ -23,6 +23,7 @@ const BROWSE_ERROR_PATTERNS = [
   /Exit code 1/,
   /ERROR: browse binary not found/,
   /Server failed to start/,
+  /no such file or directory.*browse/i,
 ];
 
 export async function runSkillTest(options: {