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>

Taskfile.yml

@@ -4,6 +4,7 @@ vars:
   BIN: ./bin/releaser
   PKG: ./...
   FUZZ_TIME: 30s
+  GEEKDOC_VERSION: "v4.1.1"
 
 tasks:
   default:
@@ -105,3 +106,23 @@ tasks:
       TAG: '{{.TAG | default "releaser:dev"}}'
     cmds:
       - docker run --rm {{.TAG}} {{.CLI_ARGS}}
+
+  docs:setup:
+    desc: Download Geekdoc theme into docs/themes/geekdoc/
+    cmds:
+      - mkdir -p docs/themes/geekdoc
+      - curl -sSL "https://github.com/thegeeklab/hugo-geekdoc/releases/download/{{.GEEKDOC_VERSION}}/hugo-geekdoc.tar.gz" | tar xz -C docs/themes/geekdoc
+    status:
+      - test -f docs/themes/geekdoc/theme.toml
+
+  docs:serve:
+    desc: Serve docs locally with live reload (requires hugo)
+    deps: [docs:setup]
+    cmds:
+      - hugo server --source docs
+
+  docs:build:
+    desc: Build docs to docs/public/ (requires hugo)
+    deps: [docs:setup]
+    cmds:
+      - hugo --source docs --destination public --minify