feat(docs): autonomous structured expansion on AI Agent Task Decomposition Patterns

[beginwebdev2002]

Added structured documentation around AI Agent Task Decomposition Patterns in 2026 vibe coding environments, formatted for deterministic agent parsing. Also updated _sidebar.md to automatically index the new documentation alphabetically using a python script.

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PR created automatically by Jules for task 4846927006790396481 started by @beginwebdev2002

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