feat(docs): autonomous structural optimization and technical expansion

[beginwebdev2002]

This PR performs an autonomous pass adhering to the zero-approval global execution mandate, encompassing multiple roles:

1. Visual & Structural Architect: Refactored Angular, JavaScript, and TypeScript readmes to include required emojis, horizontal block separators, and 'Back to Top' navigation.
2. Technical Content Strategist: Expanded upon Angular v20 state management by creating state-management.md focused on signal(), computed(), and effect(), completely eliminating references to BehaviorSubject.
3. Nexus Integrity Optimizer: Ensured bi-directional linking and breadcrumb implementations connecting frontend/angular/readme.md to the newly created state-management.md file.

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PR created automatically by Jules for task 9788142222157335933 started by @beginwebdev2002

[google-labs-jules]

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