Add lightweight self-hosted Hugo CMS with GitHub API backend

Implements a Go-based CMS for editing Hugo posts and uploading images
via the GitHub REST API, with no database and Git as the source of truth.

Features:
- Single admin auth with bcrypt password and signed session cookies
- Dashboard, post listing with search, create/edit with EasyMDE editor
- Media library for static/uploads/ with drag-drop and clipboard paste
- Client-side autosave, unsaved changes warning, dark mode, responsive UI
- Modular packages for auth, github, posts, media, session, and handlers

Co-authored-by: codegirl007 <s.raide@gmail.com>

cms/.env.example

@@ -0,0 +1,14 @@
+# GitHub API credentials
+GITHUB_TOKEN=ghp_your_token_here
+GITHUB_OWNER=your-username
+GITHUB_REPO=your-hugo-repo
+GITHUB_BRANCH=master
+
+# Session and authentication
+SESSION_SECRET=change-me-to-a-random-string
+ADMIN_USERNAME=admin
+ADMIN_PASSWORD_HASH=$2a$10$example_bcrypt_hash_here
+
+# Server
+ADDR=:8080
+COOKIE_SECURE=true