feat(android): update to 2.6.7

[dcrawbuck]

Add Android 2.6.7 release notes to the changelog to update the SDK documentation.

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Note

Updates Android SDK docs for 2.6.7 and expands guidance on permissions and purchase data flows.

• Adds 2.6.7 changelog with permission granting from paywalls, PaywallPreloadStart/Complete events, and various fixes
• New advanced guide: guides/advanced/request-permissions-from-paywalls.mdx (+ linked in meta.json) showing how to trigger runtime permissions and handle results/events
• Expands SDK reference: documents Superwall.instance.customerInfo flow and getCustomerInfo(), new delegate callbacks (customerInfoDidChange, userAttributesDidChange), and new events (Permission*, CustomerInfoDidChange, PaywallPreload*) with example handlers
• Enhances quickstart tracking-subscription-state.mdx with CustomerInfo usage patterns
• Bumps displayed SDK version to 2.6.7 in content/docs/android/index.mdx and sdk-reference/index.mdx

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[cursor]

Cursor Agent can help with this pull request. Just @cursor in comments and I'll start working on changes in this branch.
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