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>

CHANGELOG.md

@@ -2,6 +2,56 @@
 
 All notable changes to Armature are documented here.
 
+## v0.6.11 — CSS Deduplication
+
+One class per concept. The old `primitives.css` button, toast, popup-menu,
+dropdown, and tabs systems are retired. `sw-primitives.css` is the single
+source of truth for all Preact component styles.
+
+### Changed
+
+- **Buttons**: All 29 files migrated from `.btn-primary` / `.btn-small` /
+  `.btn-danger` / `.btn-ghost` / `.btn-md` / `.btn-sm` to the BEM-style
+  `.sw-btn .sw-btn--{variant} .sw-btn--{size}` system.
+- **Toasts**: Old `.toast-container` / `.toast` CSS deleted. SDK's
+  `sw.toast()` API already used `.sw-toast-*` classes — no JS changes.
+- **Popup menus**: Old `.popup-menu` / `.popup-menu-item` CSS deleted
+  (unused — `.sw-menu` is the active system).
+- **Dropdown collision resolved**: Old `.sw-dropdown` (styled `<select>`)
+  deleted from `primitives.css`. The `sw-primitives.css` custom dropdown
+  component (`.sw-dropdown` with BEM sub-elements) is authoritative.
+- **Tabs collision resolved**: Old `.sw-tabs` / `.sw-tab-btn` deleted from
+  `primitives.css`. The `sw-primitives.css` scrollable tabs component
+  (`.sw-tabs__tab`) is authoritative.
+- **`.settings-section` collision resolved**: Removed duplicate definition
+  from `modals.css`. The `surfaces.css` card-style definition is
+  authoritative; `.settings-content .settings-section` override resets
+  card styling for flat settings layouts.
+
+### Added
+
+- `.sw-btn--success` variant in `sw-primitives.css` (green action button).
+- `--bg-active` CSS variable in both dark/light themes (`variables.css`).
+- `scripts/audit-css-collisions.sh` — finds duplicate class selectors
+  across kernel CSS files and outputs a JSON collision report.
+
+### Fixed
+
+- `packages/sdk-test-runner/css/main.css`: Wrong variable names
+  (`--text3` → `--text-3`, `--text2` → `--text-2`, `--bg1`/`--bg2` →
+  `--bg-raised`).
+- `packages/icd-test-runner/css/main.css`: Replaced inline button fallback
+  styles with kernel `.sw-btn` system.
+
+### Removed
+
+- Old button classes: `.btn-primary`, `.btn-small`, `.btn-danger`,
+  `.btn-full`, `.btn-ghost`, `.btn-subtle`, `.btn-sm`, `.btn-md`.
+- Old toast classes: `.toast-container`, `.toast`, `.toast.error/warning/success`.
+- Old popup menu classes: `.popup-menu`, `.popup-menu-item`, `.popup-menu-*`.
+- Old dropdown and tabs definitions from `primitives.css` that collided
+  with `sw-primitives.css`.
+
 ## v0.6.10 — Viewport Foundation
 
 Single layout model. Every surface renders inside one containment chain: