feat: add Sonar-compatible stickers

[vincenzopalazzo]

Summary

• add Sonar pack discovery, trusted pack/Signal deep links, preview, install/uninstall, and Signal import UI
• add an emoji/sticker composer picker with optimistic send, retry, exact hash-bound rendering, replies, chat previews, notifications, and transcript export
• keep protocol authority in Marmot's encrypted SQLite projection; Android only holds a bounded session asset LRU
• ship regenerated Kotlin bindings and JNI libraries for arm64, armv7, x86, and x86_64 pinned to public native commit 64dea57

Native dependency

• Depends on feat: add Sonar-compatible sticker support marmot-protocol/mdk#875
• Native PR passed three Cursor Agent Grok 4.5 review passes; all findings were fixed and the closure pass reported no findings

Privacy and security

• Signal keys are removed from the Activity/Compose input state before native import and never persisted
• only canonical HTTPS Sonar/Signal origins are routed; embedded relay hints are not trusted
• native verifies exact coordinate + shortcode + plaintext hash before any asset fetch or send
• asset bytes are capped, session-only, account-scoped, and cleared on switch/sign-out

Verification

• ./gradlew :app:testDevDebugUnitTest
• ./gradlew :app:lintDevDebug
• ./gradlew :app:ktlintCheck
• native: cargo test -p marmot-app -p marmot-uniffi -p storage-sqlite
• native: cargo clippy -p marmot-app -p marmot-uniffi -p storage-sqlite --all-targets -- -D warnings

[vincenzopalazzo]

Superseded by the upstream PR: marmot-protocol#1442