Theme-engine aesthetic: default koad:io theme + brand-variant patterns

[koad]

Context

Vulcan's 2026-04-14 interface package audit (assessments/2026-04-14-interface-package-audit.md) flagged style-basic-bitch (Astro-era base theme) as bloated. Years of accumulated CSS, much of it obsoleted by modern CSS (custom properties, :has(), container queries, @layer, logical properties). Nav CSS has already been extracted to packages/navigation.

Koad's review reframed the work: don't promote style-basic-bitch as a peer package. Either merge into theme-engine/ as a canonical default theme, or refactor to be theme-engine compliant.

The chain

```
Iris's branding guide (canonical)
→ theme-engine (consumes brand tokens, emits themes)
→ themes (koad:io default + user-built)
→ user apps (drop in, inherit brand)
```

Muse deliverable

Own theme-engine aesthetic output.

1. Default koad:io theme — the reference aesthetic. Modern CSS only, no legacy bloat, consumes Iris's brand tokens.
2. Brand-variant patterns — design patterns for how users build their own themes on top of the same engine. Shows the product story in action.

Scope

• Audit what survives from style-basic-bitch vs. what modern CSS obsoletes
• Define the contract between brand tokens (Iris) and rendered theme
• Ship a default theme that consumes the contract

Coordination

• Iris owns the canonical branding guide (brand tokens, voice, visual language) — Canonical branding guide — internal reference + user-facing asset iris#11
• Vulcan builds the pipeline and handles package rehoming — Audit and promote 27 draft interface packages vulcan#74

Not this issue

• The branding guide itself (Iris)
• Building theme-engine runtime / pipeline (Vulcan)
• Navigation styles — already in packages/navigation, don't re-duplicate