refactor(backend): optimize backend snippets for deterministic Agent parsing

[beginwebdev2002]

Replaced generic, copy-paste ⚠️ Problem boilerplates in backend documentation with context-specific technical analyses to correctly highlight risks like event loop blocking, NoSQL injection, memory leaks, and memory bloat. This aligns the repository with 2026 deterministic standards for AI agents.

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PR created automatically by Jules for task 12129639468953039274 started by @beginwebdev2002

[google-labs-jules]

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