#10508: fix(android): fix identity signature failure on Android devices

- Add EdDSA security provider to support Ed25519 key operations on older Android versions - Change client identifier from "openclaw-control-ui" to "openclaw-android" <!-- greptile_comment --> <h2>Greptile Overview</h2> <h3>Greptile Summary</h3> - Adds the `net.i2p.crypto:eddsa` provider dependency and uses it as a fallback for Ed25519 keypair generation and payload signing on Android. - Updates Android gateway client identifier from `openclaw-control-ui` to `openclaw-android` for operator connections (node connections already used `openclaw-android`). - Updates `.gitignore` to ignore `.android-sdk/*` artifacts. <h3>Confidence Score: 3/5</h3> - This PR is close, but the EdDSA fallback path may still fail on devices that need it due to algorithm/encoding mismatches and provider registration races. - Most changes are small and targeted, but the critical behavior change (Ed25519 signing fallback) appears internally inconsistent: keys may be generated/encoded via one algorithm/provider and later parsed/signed via another, which can keep returning null signatures on the exact older Android versions this aims to fix. There is also a concrete thread-safety issue around provider registration. - apps/android/app/src/main/java/ai/openclaw/android/gateway/DeviceIdentityStore.kt <!-- greptile_other_comments_section --> _{(2/5) Greptile learns from your feedback when you react with thumbs up/down!} <!-- /greptile_comment -->