Docs: Add AGENTS.md AI operating guidelines for iOS

[metalisk]

Description

Add repository-level AI agent guidelines for ADAMANT iOS in AGENTS.md.

The document now includes:

• mission and priority order for iOS agent work
• security, privacy, decentralization rules for iOS native app
• iOS platform and Swift-specific guidelines
• architecture overview and system map
• dependency injection rules (Swinject)
• testing and validation policy
• code style and quality requirements
• issue/PR conventions aligned with org standards

Related issue

Closes #936

How to test

• Review AGENTS.md content
• Verify markdown formatting
• Compare structure with Node and PWA AGENTS.md files

Notes for reviewers

Based on:

• ADAMANT Node AGENTS.md: https://github.com/Adamant-im/adamant/blob/dev/AGENTS.md
• ADAMANT PWA AGENTS.md: https://github.com/Adamant-im/adamant-im/blob/dev/AGENTS.md

Covers iOS-specific aspects:

• UIKit, MVVM, Coordinator patterns
• Swinject DI container
• Core Data, Keychain security
• App Store compliance
• Multi-platform support (iPhone, iPad, macOS M-series)
• Wallet parameters from https://github.com/Adamant-im/adamant-wallets

[adamantmm]

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