docs: add progressive disclosure documentation

[plutoless]

Summary

• Adds docs/ai/ progressive disclosure tree (L0 repo card, 8 L1 summaries, 2 L2 deep dives, RECIPE.md, test-results.md) per the AgoraIO-Community/ai-devkit standard.
• Adds AGENTS.md — coding-agent handbook with How to Load, system shape, session ordering, env vars, patterns, anti-patterns, commands, done criteria, Git Conventions, and Doc Commands.
• Adds CLAUDE.md — one-liner redirect to AGENTS.md.

Stack documented

• Android: Kotlin 2.0.20 / Jetpack Compose (BOM 2024.09.02) / AGP 8.5.2 — Agora RTC 4.5.1 + RTM 2.2.3 + vendored ConversationalAIAPI toolkit.
• Backend: Python FastAPI token service — cascading DeepgramSTT → OpenAI (Agora-managed, keyless) → MiniMaxTTS pipeline.

Test results

• 15/15 questions pass across 5 categories (Setup, Test/Run, Conventions, Development, Deep Dive).
• 35 relative links checked, 0 broken.
• Pre-existing server test failure noted in test-results.md (test_agent_construction.py — incomplete 2.3.x migration in agent.py); not a docs issue.

Files changed

Only AGENTS.md, CLAUDE.md, and docs/ — no source or build files modified.