Use nixica 0.1.0 for flake infrastructure

Summary

• Replace direct flake-parts, import-tree, and treefmt-nix inputs with nixica 0.1.0
• Use nixica.lib.mkFlake for flake outputs instead of calling flake-parts directly
• Use nixica.formatting for treefmt configuration
• Route flake-parts module imports through nixica.inputs.flake-parts
• Update strict-inputs exceptions for new input structure