Remove Studio Code turn cap handling

[youknowriad]

Summary

• stop passing a default maxTurns value from the agent wrapper
• remove the special max-turns result path from the JSON adapter, UI, and command flow
• keep explicit maxTurns support for callers that provide it
• update unit coverage for the default and explicit SDK passthrough behavior

Testing

• npx eslint --fix on the modified CLI files
• npm test -- apps/cli/ai/tests/agent.test.ts apps/cli/commands/ai/tests/ai.test.ts
• npm run typecheck

[wpmobilebot]

📊 Performance Test Results

Comparing fe4cd8b vs trunk

app-size

Metric	trunk	fe4cd8b	Diff	Change
App Size (Mac)	1454.55 MB	1454.49 MB	0.06 MB	⚪ 0.0%

site-editor

Metric	trunk	fe4cd8b	Diff	Change
load	1801 ms	1848 ms	+47 ms	⚪ 0.0%

site-startup

Metric	trunk	fe4cd8b	Diff	Change
siteCreation	8092 ms	8112 ms	+20 ms	⚪ 0.0%
siteStartup	4950 ms	4954 ms	+4 ms	⚪ 0.0%

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Results are median values from multiple test runs.

Legend: 🟢 Improvement (faster) | 🔴 Regression (slower) | ⚪ No change (<50ms diff)