chore: add topic descriptions for orphaned topics

[oscarbol09]

What

Adds a concise, single-paragraph description to 32 topics that only had a title and no content, following the contributing guidelines (English, one paragraph, no resource changes).

The affected topics were identified as empty (0 characters of description) across 10 roadmaps:

Roadmap	Topics
aspnet-core	Bogus, Distributed Lock, Frameworks, GitLab CI/CD, Mapperly, Marten, .NET Aspire (x2), .NET MAUI, Respawn, Scalar, Testcontainers
datastructures-and-algorithms	A* Algorithm, Cyclic Sort, Fast and Slow Pointers, Island traversal, Kth Element, Merge Intervals, Multi-threaded
software-design-architecture	Architectural Patterns, Architectural Principles, Design Principles
react-native	Listings, ListViews, View
flutter	AppStore, Firebase
blockchain	TVM-Based
devrel	Video Production
power-bi	Hierarchies
react	useState
spring-boot	Micrometer

Notes:

• power-bi/hierarchies had no content at all, not even a title — added the missing # Hierarchies heading as well.
• Resource links were intentionally left untouched; this PR only adds descriptions.

Verification

• All 32 files pass the content validation script (npm run validate:content -- --files=..., exit 0).
• prettier --check passes.