Root Intent-5 buyer preview

Publishes the root Intent-5 buyer preview route:

• https://trungcodeer.github.io/intent-5/
• https://trungcodeer.github.io/intent-5.json
• https://trungcodeer.github.io/intent-5.txt

The route gives four public buyer-intent samples before routing a qualified buyer to the exact 5 USD PayPal checkout. Fulfillment remains gated on seller-side evidence or PAYPAL_PAYMENT_VERIFIED=true.