release(android): 1.18.1 browser sign-in patch

[Codename-11]

Scope

• Selective Android 1.18.1 patch from immutable android-v1.18.0 production tag.
• Carries the verified browser sign-in foreground fix and provider-specific callback pages from fix(android): retain browser sign-in callback in foreground #657, plus Android version 59 and release notes.
• Excludes post-1.18.0 plugin log fixes and desktop documentation on dev.

Gates

• Merge fix(android): retain browser sign-in callback in foreground #657 into dev after its exact-head checks pass.
• Run this PR's exact-head checks and local release metadata/presentation checks.
• Update the Play specialUse declaration and review recording for browser sign-in before Play submission.
• Complete private Play preflight on the final untagged main tree before release approval/tag publication.