Block development: static vs dynamic blocks

[luisherranz]

What

Teach the block-development skill how to choose between static and dynamic rendering when creating a new block, and add eval scenarios to verify the decision.

Why

The skill had no guidance on this decision. Agents would default to whichever pattern they'd seen most in training data, leading to inconsistent choices: sometimes static when dynamic was clearly needed (e.g., Interactivity API blocks, blocks in template parts), and sometimes dynamic for simple presentational blocks where static is fine. A priority-ordered checklist eliminates the guesswork.

How

• Add references/static-vs-dynamic-blocks.md: a "first YES wins" decision checklist covering external data, evolving markup, Interactivity API, block themes, server-side needs, content portability, and simple presentational blocks.
• Update SKILL.md step 3 ("Pick the right block model") to point to the new reference and simplify the interactivity guidance into a single line that loads wp-interactivity-api.
• Add 8 new eval scenarios (6 dynamic, 2 static) that each test a different decision point from the checklist, including one adversarial case where a lower-priority signal (portability) conflicts with a higher-priority one (server-side auth).
• Update the existing block-create-interactive-inner-blocks eval to include the static-vs-dynamic decision step, since Interactivity API requires dynamic rendering.

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[luisherranz]

@Jameswlepage, any guidance on how to run the evals to test that they work?