DOC-6661 feature store use case

[andy-stark-redis]

Not finished yet - this is just to get the Bugbot feedback as early as possible.

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Note

Medium Risk
Large documentation and demo surface with concurrency-sensitive worker/reset patterns and Redis 7.4 HEXPIRE semantics; incorrect examples could mislead operators, but no production runtime or auth changes.

Overview
Adds a new Redis feature store use-case hub and client walkthroughs with runnable fraud-scoring demos: per-entity hashes at fs:user:{id}, batch HSET + key EXPIRE, streaming updates with HEXPIRE / HTTL (Redis 7.4+), HMGET inference, and pipelined batch reads, plus a background streaming worker (bulk-load, pause/resume, reset, inspect UI).

The diff shown includes substantial Go (featurestore package, cmd/demo_server / build_features, demo_server.go) and .NET (ASP.NET minimal API, FeatureStore, StreamingWorker, shared HTML) implementations with explicit handling of per-field HEXPIRE reply codes, pause + wait_for_idle around reset, and worker lifecycle. The hub page links nine client ports (Python through Ruby); other languages may land in the same PR beyond the excerpt.

Porting skill maintenance: documents the feature-store reference in redis-use-case-ports, adds audit-checklist rows 35–37 (HEXPIRE/HTTL reply checking, in-flight flag before pause check, bounded worker stop), and a streaming-worker / background-task section in redis-conventions.md (including per-client HEXPIRE pipeline reply shapes).

Also lists Feature store on content/develop/use-cases/_index.md and broadens .gitignore to ignore build/vendor output under all content/develop/use-cases/** demos (Rust, Java, .NET, PHP, Ruby).

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[jit-ci]

🛡️ Jit Security Scan Results

✅ No security findings were detected in this PR

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[github-actions]

Staging links:
https://redis.io/docs/staging/DOC-6661-feature-store-use-case/develop/use-cases/
https://redis.io/docs/staging/DOC-6661-feature-store-use-case/develop/use-cases/feature-store/
https://redis.io/docs/staging/DOC-6661-feature-store-use-case/develop/use-cases/feature-store/dotnet/
https://redis.io/docs/staging/DOC-6661-feature-store-use-case/develop/use-cases/feature-store/go/
https://redis.io/docs/staging/DOC-6661-feature-store-use-case/develop/use-cases/feature-store/java-jedis/

[dwdougherty]

Just one material comment; otherwise, LGTM.

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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