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/layout-columns.md

@@ -0,0 +1,80 @@
+---
+name: layout-columns
+description: Multi-column layout with columns utility for masonry-like or newspaper layouts
+---
+
+# Columns
+
+Utilities for CSS multi-column layout. Content flows into multiple columns within a single element.
+
+## Usage
+
+### By number of columns
+
+```html
+<div class="columns-3 gap-8">
+  <img class="aspect-3/2" src="1.jpg" />
+  <img class="aspect-square" src="2.jpg" />
+  <!-- Content flows into 3 columns -->
+</div>
+```
+
+### By column width
+
+Use container scale for ideal column width; column count adjusts automatically:
+
+```html
+<div class="columns-3xs gap-4">...</div>
+<div class="columns-sm gap-6">...</div>
+<div class="columns-md">...</div>
+```
+
+### Column gap
+
+Use `gap-*` utilities for space between columns:
+
+```html
+<div class="columns-3 gap-8">...</div>
+```
+
+### Responsive
+
+```html
+<div class="columns-2 gap-4 sm:columns-3 sm:gap-8">...</div>
+```
+
+### Custom value
+
+```html
+<div class="columns-[30vw]">...</div>
+<div class="columns-(--my-columns)">...</div>
+```
+
+### Column / page breaks
+
+Use with multi-column or print layouts:
+
+```html
+<div class="columns-2">
+  <p>Content...</p>
+  <p class="break-after-column">Force break after this</p>
+  <p>Next column...</p>
+</div>
+```
+
+- `break-after-column` / `break-before-column` - column break
+- `break-after-page` / `break-before-page` - page break (print)
+- `break-after-avoid` / `break-inside-avoid` - avoid breaking
+
+## Key Points
+
+- `columns-<n>` - fixed number of columns (e.g. `columns-3`)
+- `columns-3xs` through `columns-7xl` - column width from container scale
+- `columns-auto` - auto columns
+- `gap-*` controls column gap (same as flex/grid gap)
+- Use for magazine-style layouts, image galleries, long text
+
+<!--
+Source references:
+- https://tailwindcss.com/docs/columns
+-->