Fix /findSimilar curl example: wrap text in contents object

[mfine15]

Summary

Fixes the curl example for the /findSimilar endpoint. The text parameter must be wrapped in a contents object for the raw API - using "text": true at the top level is silently ignored.

The Python and JS SDK examples are correct as-is because the SDKs handle this transformation internally.

Review & Testing Checklist for Human

• Verify by running the curl example that contents: {text: true} actually returns text content in results
• Confirm the old format "text": true at top level was indeed being ignored

Notes

Part of a docs audit finding behavior mismatches between documentation and actual API behavior.

Link to Devin run: https://app.devin.ai/sessions/616457e78aea475481e0607e4f176b40
Requested by: Michael Fine (@mfine15), PRs requested by Ishan Goswami

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