Add project configuration and build assets

- .gitignore: Ignore node_modules, .env, dist, .wrangler
- .env.example: Environment variable template
- package.json, package-lock.json: Tailwind CSS build setup
- src/input.css: Tailwind source file
- style.css: Production Tailwind build
- og-image.png: Open Graph image for social sharing

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.env.example

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+# HashiCorp Vault Configuration
+VAULT_ADDR=https://your-vault-server:8200
+VAULT_TOKEN=hvs.your_root_or_accessor_token
+VAULT_NAMESPACE=admin # (옵션) 기업용/클라우드 사용 시 필요
+
+# API Path Example (KV Engine v2)
+# 예: secret/data/anvil-hosting -> VAULT_SECRET_PATH=secret/data/anvil-hosting
+VAULT_SECRET_PATH=secret/data/production