docs(releaser): release v1.5.1 — documentation site, fuzzing completeness

- Add Hugo + Geekdoc documentation site (docs/): installation, CLI
  reference, configuration, CI integration, and changelog pages; explicit
  menu bundle nav so all pages appear in the sidebar on every page
- Add Gitea CI workflow (.gitea/workflows/docs.yml): builds on push to
  main when docs/** changes, deploys minified site to gh-pages branch
- Add docs:setup / docs:serve / docs:build Taskfile tasks; theme bundle
  downloaded at build time (not committed)
- Add FuzzUpdate to internal/changelog and FuzzWriteVersion to
  internal/node to complete fuzz coverage for all file-rewriting packages
- Add fuzzing completeness guidelines to CLAUDE.md: authoritative table,
  exempt-package rationale, seed corpus rules

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docs/data/menu/main.yaml

@@ -0,0 +1,16 @@
+main:
+  - name: Installation
+    ref: /installation
+    weight: 10
+  - name: CLI Reference
+    ref: /usage
+    weight: 20
+  - name: Configuration
+    ref: /configuration
+    weight: 30
+  - name: CI Integration
+    ref: /ci-integration
+    weight: 40
+  - name: Changelog
+    ref: /changelog
+    weight: 50