pelican migration support

[Luxxy-GF]

Added Pelican import support to the import command group.

Changes:

• backend/src/commands/import/mod.rs now registers a new pelican import subcommand alongside the existing pterodactyl importer.
• backend/src/commands/import/pelican.rs adds the Pelican-specific importer implementation.

What the Pelican importer does:

• Loads the Pelican .env file and connects to the source database.
• Imports shared panel data like settings, users, SSH keys, nodes, eggs, servers, databases, backups, schedules, allocations, and mounts.
• Adapts Pelican schema differences from Pterodactyl, including:
  • role-based admin detection
  • MFA secret handling
  • synthetic locations and nests derived from Pelican tags
  • Pelican mountables relations
  • Pelican egg startup_commands

Why:

• This adds a direct migration path from Pelican into Calagopus without changing the existing Pterodactyl importer behavior.