docs: glass reads as the lib's identity and default; present it as one style among many #559

The default style is solid; glass is one opt-in style. Docs, skill, AGENTS.md, README, package description, MCP/manifest text and examples still lead with glass (glass tokens, 'Glass surfaces', GlassCard/LiquidGlass up front, backdrop-filter as critical rule 2, material=glass examples). An AI reading them makes everything glassy. Audit + rewrite: theme-driven, style is one knob, glass-specific rules scoped to a 'Glass and frosted styles' section, deprecated GlassCard/GlassSurface documented as deprecated.