Fix documentation snippets

[fallintoplace]

Summary

• fix invalid valkeyClusterOptions designated-initializer examples in cluster.md
• fix the gencommands.py link in cluster.md
• fix the valkeyCommandArgv snippet typo in standalone.md
• fix the valkeyReply wording typo in standalone.md

Why

Several documentation snippets were not copy-pasteable as written. The cluster docs used semicolons inside C designated initializers, one async example missed the closing ; after the initializer, the gencommands.py link pointed at the wrong directory, and standalone.md had two small typos.

Validation

• verified scripts/gencommands.py exists
• confirmed the broken strings and invalid initializer patterns are removed from docs/cluster.md and docs/standalone.md

[bjosv]

Good findings, please update the commit with a DCO, see CONTRIBUTING.md

[fallintoplace]

@bjosv I will check later today.