feat: add OpenSpec specs and changes for ASW restructure

Specs: repo-structure, 10 framework layer specs, packs, site.
Changes: repo-restructure (10 tasks), css-refactor (12 tasks),
legacy-import (proposal + triage categories).

Supersede docs/css-refactor-plan.md in favor of OpenSpec change.

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

openspec/specs/packs/spec.md

@@ -0,0 +1,46 @@
+# Spec: Packs
+
+Directory: `packs/`
+
+## Purpose
+
+Engine integration bundles. Each pack adapts ASW for a specific web server or static site generator. A pack is a self-contained directory that someone can copy into their project.
+
+## Current Packs
+
+| Pack | Purpose | Source |
+|------|---------|--------|
+| `hugo/` | Hugo theme: layouts, partials, archetypes, static assets | Legacy repo |
+| `apache/` | Autoindex styling, error pages, Apache conf snippets | Legacy repo |
+| `caddy/` | Browse template, error pages, Caddyfile snippets | Legacy repo |
+| `flask/` | Python error handler, Flask integration | Legacy repo |
+| `nginx/` | Autoindex header, error pages, Nginx conf snippets | Legacy repo |
+| `pandoc/` | HTML5 template, Lua filter for ASW output | Legacy repo |
+| `python/` | Simple Python HTTP server with ASW styling | Legacy repo |
+
+## Pack Contract
+
+Each pack directory MUST contain:
+- `README.md` — what the pack does, how to install/use it
+- All files needed for integration (conf snippets, templates, static assets)
+
+Each pack SHOULD:
+- Reference `dist/asw.css` for the framework CSS (not `src/layers/`)
+- Be self-contained — no dependencies outside the pack directory and `dist/`
+- Include example configuration
+
+## Scenarios
+
+### Given a new engine integration
+- **When** someone wants ASW support for a new engine
+- **Then** they create `packs/<engine>/` with a README and integration files
+- **And** the pack references `dist/asw.css`
+
+### Given the Hugo pack
+- **When** the ASW website is built
+- **Then** it uses `packs/hugo/` for layouts, partials, and configuration
+- **And** `site/` contains Hugo-specific overrides on top of the pack
+
+## Note
+
+The Hugo pack is special: the ASW website (`site/`) is built with it. The pack provides the base; `site/` adds content and any site-specific customization. This is both a real integration and a living example.