v0.1.0-beta.3

• Name the incoming-payment product PayIn; keep Payout/refunds in a conditional roadmap.
• Add browser-side signed-request verification and optional independent public-signer comparison.
• Introduce a white/purple checkout with payment-language progress, advanced details,
  local request-link QR and copy/download handoff. No wallet connector is implied.
• Expose additive paymentStage and overpaymentAmountAtomic public presentation fields.
• Preserve FINALIZED + SPENDABLE + MATCHED acceptance, existing intent statuses and payment.confirmed.
• Add reference-payer readiness with exact balance/fee-budget arithmetic; no submission or estimated wait.
• Accept additive public request fields in the payer while retaining signed-field verification.
• Document Payment Request v1, privacy boundaries and separate payer usability targets.

These changes follow published beta.2. No new real-money pilot, wallet compatibility
or independent usability result is claimed.

The reference payer is version 0.1.0-alpha.1. Existing beta.0–beta.2 backup manifests
remain restorable. Build/install the merchant and payer from this same source tag.

Full Changelog: v0.1.0-beta.2...v0.1.0-beta.3