chore(main): release 8.0.0-beta.3

[aao-ipr-bot]

8.0.0-beta.3

SDK 8 beta release notes are cumulative. Adopters upgrading from SDK 7 should read the SDK 7 to 8 and AdCP 3.1 to 3.2 migration guides.

Breaking changes

• beta.1: ADCPClient.handle_webhook() no longer accepts unsigned MCP callbacks by default. Configure webhook_secret for legacy HMAC or use WebhookReceiver.
• beta.3: Low-level sign_request() and async_sign_request() now require signing_profile_version. ADCPClient derives it from the trusted AdCP version pin.

Highlights across beta.1 to beta.3

• beta.1 aligns safety and asset APIs with JavaScript SDK v13, including AssetInstance.
• beta.2 bundles AdCP 3.2.0-beta.0 and the compact/proposal lifecycle: list, request/refine/decline proposals, direct buy, proposal acceptance, and media-buy control.
• beta.3 adds public v30/v31/v32 models and portable MCP schemas, BrandIdentity, negotiated signing profiles, and consistent MCP advertisement/dispatch version pinning.

Higher-level proposal lineage, digest, constraint, rollback, and orchestration helpers remain tracked in #1023.

Implementation: #1038.

[aao-secretariat]

Ladon verdict: Approve

Approve — release-please version bump for 8.0.0-beta.3.

This PR touches only release-management files (.release-please-manifest.json, CHANGELOG.md, pyproject.toml) with no source or public-surface changes. Version fields are consistent (manifest 8.0.0-beta.3 ↔ pyproject PEP 440 8.0.0b3), the referenced migration guides exist at repo root, and the BREAKING CHANGES prose matches the underlying feat! history.

Decision-table walkthrough:

• No critical/high findings (row 1 n/a).
• gated_paths is false (row 2 n/a).
• high_risk is false; no deletions/modifications triggers (rows 3–5 n/a).
• No prior decision (row 6 n/a).
• No no-auto-approve team match (row 7 n/a).
• Zero medium findings (row 8 n/a).
• Falls through to row 9 → approve.

Note: review_decision is REVIEW_REQUIRED, but since gated_paths is false this does not force escalation or block approval.