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/internal/config/config.go

@@ -0,0 +1,62 @@
+package config
+
+import (
+	"fmt"
+	"os"
+)
+
+// Config holds all environment-based configuration for the CMS server.
+type Config struct {
+	GitHubToken       string
+	GitHubOwner       string
+	GitHubRepo        string
+	GitHubBranch      string
+	SessionSecret     string
+	AdminUsername     string
+	AdminPasswordHash string
+	Addr              string
+	CookieSecure      bool
+}
+
+// Load reads configuration from environment variables.
+func Load() (*Config, error) {
+	cfg := &Config{
+		GitHubToken:       os.Getenv("GITHUB_TOKEN"),
+		GitHubOwner:       os.Getenv("GITHUB_OWNER"),
+		GitHubRepo:        os.Getenv("GITHUB_REPO"),
+		GitHubBranch:      envOrDefault("GITHUB_BRANCH", "master"),
+		SessionSecret:     os.Getenv("SESSION_SECRET"),
+		AdminUsername:     os.Getenv("ADMIN_USERNAME"),
+		AdminPasswordHash: os.Getenv("ADMIN_PASSWORD_HASH"),
+		Addr:              envOrDefault("ADDR", ":8080"),
+		CookieSecure:      envOrDefault("COOKIE_SECURE", "true") == "true",
+	}
+
+	if cfg.GitHubToken == "" {
+		return nil, fmt.Errorf("GITHUB_TOKEN is required")
+	}
+	if cfg.GitHubOwner == "" {
+		return nil, fmt.Errorf("GITHUB_OWNER is required")
+	}
+	if cfg.GitHubRepo == "" {
+		return nil, fmt.Errorf("GITHUB_REPO is required")
+	}
+	if cfg.SessionSecret == "" {
+		return nil, fmt.Errorf("SESSION_SECRET is required")
+	}
+	if cfg.AdminUsername == "" {
+		return nil, fmt.Errorf("ADMIN_USERNAME is required")
+	}
+	if cfg.AdminPasswordHash == "" {
+		return nil, fmt.Errorf("ADMIN_PASSWORD_HASH is required")
+	}
+
+	return cfg, nil
+}
+
+func envOrDefault(key, fallback string) string {
+	if v := os.Getenv(key); v != "" {
+		return v
+	}
+	return fallback
+}