What does this PR do?

Nexus docs update:

• Rewrite evaluate page with production social proof (Duolingo, Netflix, Miro), outcome-focused benefits, and new light/dark SVG decision trees
• Rewrite Nexus encyclopedia for clarity and concision
• Add new Nexus Patterns page documenting collocated and router-queue deployment patterns
• Expand payload encryption docs with three cross-Namespace approaches: shared key, KMS key ID in metadata, and endpoint-specific wrapper types
• Add "Use the Temporal Client for Signals, Queries, and Updates" section with code examples in all five SDK guides (Go, Java, Python, TypeScript, .NET)
• Add circuit breaker guidance across all SDK guides - handlers should be reliable since it trips after 5 consecutive errors
• Condense all Cloud Nexus pages (index, security, limits, observability, latency, pricing) into scannable bullet lists linking to canonical sources
• Add caution block for changing Endpoint target Namespace with drain recommendation, and document registry access control defaults
• Update Cloud Namespace best practices to recommend Nexus instead of "Workflows should be in the same Namespace"
• Remove deprecated use-cases page, fix broken links, fix typos, standardize sample names, and add Python/TypeScript/.NET to all SDK link lists

┆Attachments: EDU-5974 Nexus docs update