Add before-you-build planning skill

[bin1874]

Summary

Adds a small before-you-build planning skill for pressure-testing product ideas and major feature requests before implementation starts.

Why it fits

The library already includes planning and decision-support skills such as roadmap prioritization, vendor evaluation, and system design. This adds a pre-build product-risk checkpoint for founders, PMs, and senior developers who are about to turn an idea into code.

Scope

• Adds skills/planning/before-you-build/SKILL.md
• Adds the skill to the Planning section in README.md
• Keeps the skill concise and implementation-agnostic

Validation

• Ran git diff --check

[gemini-code-assist]

Code Review

This pull request introduces a new skill called before-you-build under skills/planning/ to pressure-test product ideas or features before implementation. The review feedback suggests shortening the descriptions in both the README.md and the skill's frontmatter to maintain consistency with existing skills. Additionally, it recommends updating the quality bar instructions so that the LLM makes reasonable assumptions and lists clarifying questions instead of simply asking questions when an idea is too broad.

[gemini-code-assist]

The description for the before-you-build skill is significantly longer than the other descriptions in this section, which are typically around 60 characters. Consider shortening it to maintain visual consistency and readability, for example:

• before-you-build: Pressure-test a product idea or feature for key risks before implementation.

[gemini-code-assist]

The frontmatter description is quite long compared to other skills in the repository. Shortening it to focus on the core purpose and target audience will align it better with the existing style.

Suggested change

	description: Review a product idea or feature before implementation by identifying the biggest demand, positioning, monetization, retention, and distribution risks. Use when a senior developer or founder wants to build a new product, landing page, MVP, or major feature but needs a reality check first.
	description: Pressure-test a product idea or feature for key risks before implementation. Use when a founder or developer needs a reality check before building.

[gemini-code-assist]

Instructing the LLM to simply ask questions when an idea is too broad can lead to incomplete or unhelpful single-turn responses. It is better to have the LLM make reasonable assumptions to proceed with the analysis while explicitly listing the clarifying questions needed to validate those assumptions.

Suggested change

	- If the idea is too broad, ask who it is for, when they use it, and what painful problem it replaces.
	- If the idea is too broad, make reasonable assumptions to narrow it down for the analysis, and clearly list the clarifying questions needed to validate those assumptions.