Add: Add BLE device continuous scan feature for Android

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Background

• My app (iBeacon triangulation) requires continuous BLE device scanning to detect nearby beacons
• The existing plugin had no scanning capability

Changes

• Add start/stop commands for continuous BLE device scanning
• Emit device discovery events with device info (name, address, RSSI, etc.)
• Implement Android BLE scanning across Kotlin, Rust, and TypeScript layers
• Add permission definitions for new scan commands

Scope

• 12 files changed, +437 / -7 lines
• Rust: src/commands.rs, src/mobile.rs, src/android_init.rs, src/bluetooth.rs, src/lib.rs, src/error.rs, src/models.rs
• Android: android/src/main/java/ExamplePlugin.kt
• JS: guest-js/index.ts, guest-js/types.ts
• Config: Cargo.toml, permissions/default.toml