Feat v0.6.11 CSS deduplication (#46)

Retire old primitives.css button/toast/popup-menu/dropdown/tabs systems.
sw-primitives.css is now the single source of truth.

- Migrate 29 files from .btn-* to .sw-btn .sw-btn--{variant} .sw-btn--{size}
- Delete old toast, popup-menu, dropdown, tabs CSS (no JS references)
- Resolve .sw-dropdown and .sw-tabs class name collisions
- Resolve .settings-section duplicate (modals.css removed, surfaces.css authoritative)
- Add .sw-btn--success variant, --bg-active CSS variable
- Fix sdk-test-runner wrong variable names, icd-test-runner button fallbacks
- Add scripts/audit-css-collisions.sh

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ROADMAP.md

@@ -1,6 +1,6 @@
 # Armature — Roadmap
 
-## Current: v0.6.10 — Viewport Foundation
+## Current: v0.6.11 — CSS Deduplication
 
 Self-hosted extensible platform. Auth, identity, packages, Starlark sandbox,
 storage, realtime, and ops are kernel primitives. Everything else is an extension.