developing-blockninja-plugins: font size hooks + pluginsdk path refresh
Two changes bundled (shared-file bundling, solo-on-main):
- Theme font size hook contract from cms ADR 0029: bn-* class hooks,
var(--fs-<key>, fallback) consumption, preserve hooks in re-skins,
wrap hardcoded font-size declarations, republish caveat. New section
in theme-overrides.md, summary + pointer in SKILL.md.
- Pre-existing uncommitted SKILL.md refresh: block/core references
migrated to block/pluginsdk and cms/docs/abi/ doc paths (P3
proto-first SDK program), description line updated to match.
Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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