feat: add new OpenSpec skills for change management and onboarding

- Created `openspec-ff-change` skill for fast-forward artifact creation.
- Introduced `openspec-new-change` skill for structured change creation.
- Developed `openspec-onboard` skill for guided onboarding through OpenSpec workflow.
- Added `openspec-sync-specs` skill for syncing delta specs to main specs.
- Implemented `openspec-verify-change` skill for verifying implementation against change artifacts.
- Updated `.gitignore` to exclude OpenSpec generated files.
- Added `skills-lock.json` to manage skill dependencies.

.agents/skills/tailwindcss/references/features-upgrade.md

@@ -0,0 +1,91 @@
+---
+name: features-upgrade
+description: Migrating from Tailwind CSS v3 to v4
+---
+
+# Upgrade Guide (v3 → v4)
+
+Key changes when upgrading from Tailwind CSS v3 to v4. Use the automated upgrade tool when possible.
+
+## Upgrade Tool
+
+```bash
+npx @tailwindcss/upgrade
+```
+
+Requires Node.js 20+. Run in a new branch, review diff, test. Handles most migration automatically.
+
+## Installation Changes
+
+- **PostCSS**: Use `@tailwindcss/postcss`; remove `postcss-import` and `autoprefixer` (handled by v4)
+- **Vite**: Prefer `@tailwindcss/vite` over PostCSS
+- **CLI**: Use `npx @tailwindcss/cli` instead of `npx tailwindcss`
+
+## Import Change
+
+```css
+/* v3 */
+@tailwind base;
+@tailwind components;
+@tailwind utilities;
+
+/* v4 */
+@import "tailwindcss";
+```
+
+## Renamed Utilities
+
+| v3 | v4 |
+|----|-----|
+| `shadow-sm` | `shadow-xs` |
+| `shadow` | `shadow-sm` |
+| `rounded-sm` | `rounded-xs` |
+| `rounded` | `rounded-sm` |
+| `blur-sm` | `blur-xs` |
+| `blur` | `blur-sm` |
+| `outline-none` | `outline-hidden` |
+| `ring` | `ring-3` |
+
+## Removed / Replaced
+
+- `bg-opacity-*`, `text-opacity-*`, etc. → use `bg-black/50`, `text-black/50`
+- `flex-shrink-*` → `shrink-*`
+- `flex-grow-*` → `grow-*`
+- `overflow-ellipsis` → `text-ellipsis`
+
+## Important Modifier
+
+```html
+<!-- v3: ! at start -->
+<div class="!bg-red-500">
+
+<!-- v4: ! at end -->
+<div class="bg-red-500!">
+```
+
+## Ring & Border Defaults
+
+- `ring` width: 3px → 1px; use `ring-3` for v3 behavior
+- `ring` / `border` default color: `currentColor` (was gray-200 / blue-500)
+- Always specify color: `ring-3 ring-blue-500`, `border border-gray-200`
+
+## Other Breaking Changes
+
+- **Space/divide selectors**: Changed from `:not([hidden]) ~ :not([hidden])` to `:not(:last-child)`; may affect layout
+- **Variant stacking**: Left-to-right in v4 (was right-to-left)
+- **Transform reset**: `transform-none` no longer resets rotate/scale/translate; use `scale-none`, `rotate-none`, etc.
+- **Hover on mobile**: `hover` only applies when device supports hover; override with `@custom-variant hover (&:hover)` if needed
+- **Arbitrary values**: Use `bg-(--var)` not `bg-[--var]` for CSS variables
+- **theme()**: Use `theme(--breakpoint-xl)` not `theme(screens.xl)`
+- **@layer utilities/components**: Use `@utility` directive instead
+- **corePlugins, safelist, separator**: Not supported; use `@source inline()` for safelisting
+- **Sass/Less/Stylus**: v4 not designed for use with CSS preprocessors
+
+## Browser Support
+
+v4 targets Safari 16.4+, Chrome 111+, Firefox 128+. For older browsers, stay on v3.4.
+
+<!--
+Source references:
+- https://tailwindcss.com/docs/upgrade-guide
+-->