docs: update AGENTS.md hierarchy with latest structure and line counts
- Root: Add Prometheus/Metis/Momus agents, MCP architecture, 82 test files
- agents/: Document 7-section delegation and wisdom notepad
- auth/: Multi-account load balancing (10 accounts), endpoint fallback
- features/: Update background-agent 825 lines, builtin-skills 1230 lines
- hooks/: 22+ hooks with event timing details
- tools/: sisyphus-task 583 lines, LSP client 632 lines
- cli/: config-manager 725 lines, 17+ doctor checks
- shared/: Cross-cutting utilities with usage patterns
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