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-environment.test.ts

@@ -19,6 +19,7 @@ vi.mock('./db.js', () => ({
 
 vi.mock('./env.js', () => ({
   readEnvFile: mockReadEnvFile,
+  getEnv: vi.fn((key: string) => undefined),
 }));
 
 vi.mock('./codex-token-rotation.js', () => ({