feat: mobile pairing + App Store QR panel

[BitHighlander]

Summary

• Add mobile pairing flow: desktop vault derives pubkeys from KeepKey, POSTs to vault.keepkey.com relay, displays QR code + 8-char code for mobile app
• Add Mobile panel (phone icon in TopNav) with App Store download QR and "Pair Device" button
• Pubkey format matches Pioneer SDK expectations (addressNList, context, path, available_scripts_types, eip155:* wildcard)

Changes

• rpc-schema.ts — new generateMobilePairing RPC method
• index.ts — backend handler: derives BTC (3 script types), UTXO xpubs, single EVM address (all chains), cosmos/xrp/sol/tron/ton addresses; POSTs to relay
• MobilePairingDialog.tsx — full-screen overlay with QR + code + countdown timer
• MobilePanel.tsx — right drawer: App Store QR, pair button, feature overview
• TopNav.tsx — phone icon next to settings gear
• DeviceSettingsDrawer.tsx — "Pair Mobile" button in Application section
• settings.json — i18n strings for mobile panel + pairing dialog

Test plan

• Connect KeepKey, open Settings → Pair Mobile → verify QR code generates
• Scan QR with KeepKey mobile app → verify vault loads with portfolio
• Click phone icon in TopNav → verify App Store QR scans correctly
• Test "Pair Device" button in Mobile panel → opens pairing dialog
• Test with device disconnected → pair button disabled