better-auth: add v1.2.0 changelog

[cb-alish]

Document the webhook event bus feature for async processing, the shared dispatch/validator refactor, and the publish-handler error handling fix.

Adds Better Auth v1.2.0 documentation and updates the package version. The changelog covers asynchronous Chargebee webhook event processing, shared dispatch and validation refactoring, dedicated event typing, processor support, and improved publish-error handling that enables Chargebee retries.

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[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Enterprise

Run ID: 804bb4f9-766c-40a5-9c49-1bfd62d4961d

📥 Commits

Reviewing files that changed from the base of the PR and between b617dc4 and 97a1550.

📒 Files selected for processing (2)

• packages/better-auth/CHANGELOG.md
• packages/better-auth/src/version.ts

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Walkthrough

The package changelog now documents v1.2.0 Chargebee webhook processing changes, and the exported package version is updated from 1.1.0 to 1.2.0.

Changes

Webhook release

Layer / File(s)	Summary
Webhook release documentation and version packages/better-auth/CHANGELOG.md, packages/better-auth/src/version.ts	Adds v1.2.0 notes for asynchronous webhook processing, dispatch and validation updates, publish failure handling, and updates VERSION to 1.2.0.

Estimated code review effort: 1 (Trivial) | ~2 minutes

🚥 Pre-merge checks | ✅ 1

✅ Passed checks (1 passed)

Check name	Status	Explanation
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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