Initial madcat-caddy: Caddy + Cloudflare DNS + caddy-security

Forked from tengu-apps/tengu-caddy, adding:
- caddy-security plugin (OAuth 2.0, Basic Auth, JWT)
- Gitea apt registry publishing in CI
- Linux-only builds (arm64 + amd64)
- Replaces/conflicts with caddy and tengu-caddy packages

README.md

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+# madcat-caddy
+
+Caddy web server with **Cloudflare DNS** and **caddy-security** plugins built in.
+Pre-built `.deb` packages for Linux servers.
+
+## Plugins
+
+| Plugin | Purpose |
+|---|---|
+| [caddy-dns/cloudflare](https://github.com/caddy-dns/cloudflare) | DNS-01 ACME challenge via Cloudflare API |
+| [caddy-security](https://github.com/greenpau/caddy-security) | OAuth 2.0 (GitHub, Google, etc.), Basic Auth, JWT authorization |
+
+## Install
+
+### APT (Debian/Ubuntu)
+
+```bash
+# Add signing key
+sudo curl https://repos.saiden.dev/api/packages/madcat-os/debian/repository.key \
+  -o /etc/apt/keyrings/madcat-os.asc
+
+# Add repository
+echo "deb [signed-by=/etc/apt/keyrings/madcat-os.asc] https://repos.saiden.dev/api/packages/madcat-os/debian bookworm main" \
+  | sudo tee /etc/apt/sources.list.d/madcat-os.list
+
+# Install
+sudo apt update
+sudo apt install madcat-caddy
+```
+
+### Manual .deb
+
+Download from [Releases](https://github.com/madcat-os/madcat-caddy/releases):
+
+```bash
+# ARM64
+curl -fsSLO https://github.com/madcat-os/madcat-caddy/releases/latest/download/madcat-caddy_2.11.2-1_arm64.deb
+sudo dpkg -i madcat-caddy_2.11.2-1_arm64.deb
+
+# AMD64
+curl -fsSLO https://github.com/madcat-os/madcat-caddy/releases/latest/download/madcat-caddy_2.11.2-1_amd64.deb
+sudo dpkg -i madcat-caddy_2.11.2-1_amd64.deb
+```
+
+## Configuration
+
+Edit `/etc/caddy/Caddyfile`:
+
+```
+{
+    email you@example.com
+    acme_dns cloudflare {env.CF_API_TOKEN}
+}
+
+example.com {
+    reverse_proxy localhost:8080
+}
+```
+
+For Cloudflare API token:
+
+```bash
+sudo mkdir -p /etc/systemd/system/caddy.service.d
+sudo tee /etc/systemd/system/caddy.service.d/env.conf << EOF
+[Service]
+Environment="CF_API_TOKEN=your-cloudflare-api-token"
+EOF
+sudo systemctl daemon-reload
+sudo systemctl restart caddy
+```
+
+## Building
+
+```bash
+make deb ARCH=arm64
+make deb ARCH=amd64
+```
+
+## License
+
+Caddy is licensed under Apache 2.0. This packaging is MIT.