feat: auto-generated docs sidebar, Decap CMS, content migration infra

Docs restructure:
- Move flat docs into section subdirs (getting-started/, core/,
  components/, reference/) with _index.md for each
- Sidebar auto-generates from content structure — no manual menu entries
- New doc pages appear automatically when created in a section

Decap CMS:
- admin/index.html + config.yml for browser-based editing
- Local mode (npx decap-server) — no OAuth needed
- Collections for all content types: docs, articles, essays, notes, pages

Hugo head.html updated for new CSS layer filenames.
decap-server added as devDependency.

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

site/static/admin/config.yml

@@ -0,0 +1,117 @@
+# Decap CMS — ASW site content manager
+#
+# LOCAL MODE: run `npx decap-server` from site/ directory
+# No OAuth, no Forgejo auth — reads/writes files directly.
+#
+# PRODUCTION MODE: switch backend to gitea (see packs/hugo/admin/config.yml)
+
+local_backend: true
+
+backend:
+  name: git-gateway
+
+media_folder: static/images
+public_folder: /images
+
+slug:
+  encoding: ascii
+  clean_accents: true
+
+collections:
+  - name: docs-getting-started
+    label: "Docs: Getting Started"
+    folder: content/docs/getting-started
+    create: true
+    slug: "{{slug}}"
+    fields: &doc-fields
+      - { label: Title, name: title, widget: string }
+      - { label: Description, name: description, widget: string, required: false }
+      - { label: Type, name: type, widget: hidden, default: docs }
+      - { label: Weight, name: weight, widget: number, required: false, hint: "Sort order in sidebar" }
+      - { label: Date, name: date, widget: datetime, format: "YYYY-MM-DD" }
+      - { label: Tags, name: tags, widget: list, required: false }
+      - { label: AI Disclosure, name: ai-disclosure, widget: select, options: ["generated", "assisted", "none"], default: "assisted" }
+      - { label: AI Model, name: ai-model, widget: string, required: false }
+      - { label: AI Provider, name: ai-provider, widget: string, required: false, default: "Anthropic" }
+      - { label: Body, name: body, widget: markdown }
+
+  - name: docs-core
+    label: "Docs: Core"
+    folder: content/docs/core
+    create: true
+    slug: "{{slug}}"
+    fields: *doc-fields
+
+  - name: docs-components
+    label: "Docs: Components"
+    folder: content/docs/components
+    create: true
+    slug: "{{slug}}"
+    fields: *doc-fields
+
+  - name: docs-reference
+    label: "Docs: Reference"
+    folder: content/docs/reference
+    create: true
+    slug: "{{slug}}"
+    fields: *doc-fields
+
+  - name: articles
+    label: Articles
+    label_singular: Article
+    folder: content/articles
+    create: true
+    slug: "{{slug}}"
+    fields:
+      - { label: Title, name: title, widget: string }
+      - { label: Description, name: description, widget: string, required: false }
+      - { label: Date, name: date, widget: datetime, format: "YYYY-MM-DD" }
+      - { label: Tags, name: tags, widget: list, required: false }
+      - { label: AI Disclosure, name: ai-disclosure, widget: select, options: ["generated", "assisted", "none"], default: "assisted" }
+      - { label: AI Model, name: ai-model, widget: string, required: false }
+      - { label: AI Provider, name: ai-provider, widget: string, required: false, default: "Anthropic" }
+      - { label: Body, name: body, widget: markdown }
+
+  - name: essays
+    label: Essays
+    label_singular: Essay
+    folder: content/essays
+    create: true
+    slug: "{{slug}}"
+    fields:
+      - { label: Title, name: title, widget: string }
+      - { label: Description, name: description, widget: string }
+      - { label: Abstract, name: abstract, widget: text, required: false }
+      - { label: Author, name: author, widget: string, required: false }
+      - { label: Eyebrow, name: eyebrow, widget: string, required: false, default: "Essay" }
+      - { label: Type, name: type, widget: hidden, default: essay }
+      - { label: Date, name: date, widget: datetime, format: "YYYY-MM-DD" }
+      - { label: Tags, name: tags, widget: list, required: false }
+      - { label: Draft, name: draft, widget: boolean, default: true }
+      - { label: AI Disclosure, name: ai-disclosure, widget: select, options: ["generated", "assisted", "none"], default: "assisted" }
+      - { label: AI Model, name: ai-model, widget: string, required: false }
+      - { label: AI Provider, name: ai-provider, widget: string, required: false, default: "Anthropic" }
+      - { label: Body, name: body, widget: markdown }
+
+  - name: notes
+    label: Notes
+    label_singular: Note
+    folder: content/notes
+    create: true
+    slug: "{{slug}}"
+    fields:
+      - { label: Title, name: title, widget: string }
+      - { label: Date, name: date, widget: datetime, format: "YYYY-MM-DD" }
+      - { label: Tags, name: tags, widget: list, required: false }
+      - { label: Body, name: body, widget: markdown }
+
+  - name: pages
+    label: Pages
+    label_singular: Page
+    folder: content/pages
+    create: true
+    slug: "{{slug}}"
+    fields:
+      - { label: Title, name: title, widget: string }
+      - { label: Description, name: description, widget: string, required: false }
+      - { label: Body, name: body, widget: markdown }