feat: CMS-editable nav, categories taxonomy, site settings

- Move top nav from hugo.toml menus to data/nav.yml (CMS-editable)
- Add categories taxonomy alongside tags
- Add Decap CMS settings collection for nav management
- Add categories field to articles and essays in CMS config

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

site/static/admin/config.yml

@@ -17,7 +17,26 @@ slug:
   encoding: ascii
   clean_accents: true
 
+# ── Site settings (file-based collections) ───────────────────────────
+
 collections:
+  - name: settings
+    label: Settings
+    files:
+      - name: nav
+        label: Navigation
+        file: data/nav.yml
+        fields:
+          - label: Navigation Links
+            name: items
+            widget: list
+            fields:
+              - { label: Name, name: name, widget: string }
+              - { label: URL, name: url, widget: string }
+              - { label: Weight, name: weight, widget: number, hint: "Sort order (lower = first)" }
+
+# ── Content collections ──────────────────────────────────────────────
+
   - name: docs-getting-started
     label: "Docs: Getting Started"
     folder: content/docs/getting-started
@@ -66,6 +85,7 @@ collections:
       - { 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: Categories, name: categories, widget: list, required: false, hint: "e.g. framework, tutorial, deep-dive" }
       - { 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 }
@@ -88,6 +108,7 @@ collections:
       - { 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: Categories, name: categories, 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" }