Mark Redis Docs/Samples companions complete

[Skymly]

Summary

• Mark P1-RD-docs ✅ in ROADMAP after Docs PR Add RoutedEvents feature skeleton projects #15 and Samples PR Add Shared module (Core and SourceGenerators.Shared) #12.
• Update docs/design/redis.md status + follow-up checkmarks.
• Closes PRD: Observables.Redis (Pub/Sub) Feature — target 0.1.8 #169 once merged (Redis PRD fully delivered: library + 0.1.9 + Docs + Samples).

Test plan

• Docs-only diff review
• Close PRD: Observables.Redis (Pub/Sub) Feature — target 0.1.8 #169 after merge

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Note

Low Risk
Markdown-only status and link updates; no runtime, build, or API changes.

Overview
Documentation-only update to reflect that Redis tenth-domain companion work (Observables.Docs + Observables.Samples) is finished after the merged companion PRs.

In docs/ROADMAP.md, P1-RD-docs moves from ⏳ companion to ✅, with links to Docs issue/PR #14 / #15 and Samples #11 / #12.

In docs/design/redis.md, the status blurb and §12 Follow-up checkmarks are updated the same way so Redis design docs stay aligned with the roadmap (library + 0.1.9 + user docs + samples).

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