Child theme override resolution

[tayebmokni]

Summary

Implement child theme override resolution: file-by-file overrides for classic themes, (theme_id, source) chain for block themes, and deep-merge theme.json between child and parent with array merging keyed by slug (not index).

Design reference

• docs/03-theme-system.md §11 (Child Themes)
• docs/03-theme-system.md §11.2 (Override rules)
• docs/03-theme-system.md §11.3 (Resolver pseudocode)

Acceptance criteria

• Child theme manifest with gonext.parent registered and parent chain loadable
• resolveFile(theme, relPath) walks child → parent → null
• DB resolver chain (child user) → (child seed) → (parent user) → (parent seed) → core (§6.3 + child layer)
• theme.json deep-merged: child overrides parent, supports nulling out parent values
• Palette / fontFamilies / fontSizes / etc arrays merged by slug, not index
• Both functions.ts files run (parent then child)
• Patterns: union of parent + child, same-slug child wins
• Integration test: install parent + child, assert resolved outputs

Dependencies

#7, #5

Complexity

M

[tayebmokni]

Closing — shipped in the merged Wave PR. Auto-close only fires for first ref.