Map resolved CSS to canonical block style attributes (#261, #259)

[chubes4]

Closes #261
Closes #259

Problem

Core blocks were emitted with a raw inline style STRING attribute (e.g. wp:paragraph {"style":"color:var(--x)"}, wp:heading {"style":"font-size:clamp(...)"}, wp:group {"style":"padding:...;background:..."}). Core blocks expect a structured style OBJECT (style.typography/color/spacing/border) + the layout attribute, so the stored HTML diverged from each block's save() and the editor threw "This block contains unexpected or invalid content" for nearly every styled element. Only buttons were fixed previously (#241).

Fix — generalize #241 to ALL blocks

New Style/StyleAttributeMapper translates an element's resolved CSS declarations (inline + matched <style>/linked CSS) into canonical block attributes and serializes them back to the inline CSS + has-* support classes WordPress writes in save(), keeping stored markup in sync with the block.

Mapping implemented:

• typography → style.typography.{fontSize,fontWeight,lineHeight,letterSpacing,textTransform,textDecoration,fontStyle}
• color → style.color.{text,background,gradient} (+ has-text-color/has-background classes)
• spacing → style.spacing.{padding,margin} (shorthand expanded to side objects)
• border → style.border.{width,style,color,radius} (+ has-border-color)
• display:flex|grid (+ flex/grid/gap props) → the block's layout attribute

Wiring:

• presentationAttributes() now returns a canonical style object (never a string) + layout, used by every block path (group, heading, paragraph, list, quote, columns, icon, …).
• BlockFactory serializes the object for all blocks via the shared mapper.
• Buttons keep resolving from the raw merged CSS via a threaded resolvedStyle callback (ButtonStyleResolver unchanged).

Hard rule: never a raw style string on a core block

Declarations that don't map to a block support (position, inset, overflow, transform, box-shadow, background images, aspect-ratio, nav anchor/submenu CSS, …) are dropped and ride on the already-preserved className (+ carried theme/companion CSS) — they are never emitted as a style string.

Hidden-state safety (#259)

display:none / visibility:hidden / opacity:0 base states (responsive/JS-revealed) are no longer frozen onto content-bearing/interactive elements (nav, CTA) — they are normalized away and surfaced as a frozen_hidden_state diagnostic finding. Genuinely decorative / aria-hidden nodes may stay hidden.

Tests

• New "canonical block style attributes" contract (tests/contract/run.php):
  • Guard: walks every emitted block and asserts the style attr is an object or absent — never a raw string (locks in the fix / prevents regression); also asserts serialized markup carries no raw display: style.
  • Positive: styled <h2>/<p> → canonical style.typography/style.color; styled <div style="display:flex;..."> → layout.type=flex + canonical color/padding.
  • Negative: unmappable props (position/inset/overflow) → className, not a raw style string.
  • Hidden-state: <nav style="display:none"> is not frozen; frozen_hidden_state finding surfaced.
• Fixture churn (behavior fix, justified): 15 parity fixtures updated. Only the style-attribute shape changed — raw style string → canonical object / layout / dropped-to-className. No content or structure changes.
• composer test fully green (contracts, unit, 128 parity fixtures, packaging); php -l clean.

Deferred long-tail (documented)

text-align (maps to a per-block align/textAlign attribute) and blockGap/gap are dropped for now rather than emitted as raw styles — the no-raw-string guard holds. These can ride in a follow-up.

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