feat: Add support for rootless Podman execution

[arousalspoon204]

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Description

This PR introduces support for running the Pangolin stack in rootless Podman mode and allows users to configure custom HTTP/HTTPS ports during installation.

Key Changes:

• Rootless Support: Added detection for rootless environments and adjusted container capabilities (conditionally disabling SYS_MODULE when rootless).
• Configurable Ports: Users can now specify HTTP and HTTPS ports during the installation process, which are then correctly applied to the `docker-compose.yml
• Host Prerequisite Checks: The installer now proactively checks for:
  • IP Forwarding (required for VPN routing).
  • wireguard kernel module (required on the host for rootless Gerbil).
  • /dev/net/tun access permissions.
  • Unprivileged port configuration (ip_unprivileged_port_start) for Podman.
• UX Improvements: Added sudo-integration for host configuration tasks if the installer is run as a non-root user.

These changes make Pangolin more flexible for deployment on systems where root access is restricted or where standard ports (80/443) are already in use.

How to test?

1. Run as non-root: Execute the installer without sudo: go run install/main.go
2. Select Podman: Choose Podman when prompted.
3. Test Ports (Two Scenarios):
   • Scenario A (Standard Ports): Enter 80 / 443. Verify that the installer detects this and asks to configure net.ipv4.ip_unprivileged_port_start so
     Podman can bind these low ports.
   • Scenario B (Custom Ports): Enter 8080 / 8443. Verify that the generated docker-compose.yml uses these ports instead of the defaults.
4. Verify Compose: Check the generated docker-compose.yml to ensure SYS_MODULE is omitted in rootless mode.