#87 docs(readme): navbar segment demos at the top, with Android

Follow-up to #86.

• Moves the navbar segment rows demo into the top Demo section, next to the other demos, as an iOS | Android table in the same format as Pull to refresh (`width="160"`).
• Adds an Android recording from the example app's Navbar playground on an Android 36 emulator.
• Re-encodes the iOS recording at 320px (771 KB; the old file was 360px and 1.1 MB). Files: `docs/navbar-segments-ios.webp` and `docs/navbar-segments-android.webp`.
• Removes the oversized 280px image from the usage section further down.

🤖 Generated with Claude Code

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