config: add auto-compact settings for Claude and Codex agents

Claude: CLAUDE_AUTOCOMPACT_PCT_OVERRIDE=50 (~500K on 1M context)
Codex: model_auto_compact_token_limit=258000 (matching CLI default)

src/agent-runner.test.ts

@@ -54,6 +54,7 @@ vi.mock('fs', async () => {
 // Mock env
 vi.mock('./env.js', () => ({
   readEnvFile: vi.fn(() => ({})),
+  getEnv: vi.fn(() => undefined),
 }));
 
 // Create a controllable fake ChildProcess