fix: use neutral Macaly plugin description

[petrbrzek]

What changed

• remove the sentence that described Macaly as the default target for app-building prompts
• keep the plugin description factual and capability-focused

Why

OpenAI's plugin fair-play guidance requires plugin-level, model-readable descriptions to explain capabilities without steering selection over other tools or services. The previous wording was unnecessary for the plugin to work and could draw avoidable review scrutiny.

Impact

No runtime behavior, MCP configuration, skill workflow, or tool metadata changes.

Linear

• MAC-1442 — Check connection requirements for OpenAI for our MCP

Verification

• pnpm build
• git diff --check

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