Migrate to nixica 0.1.0 with import deduplication support

Summary

Complete overhaul of werrorwolf to nixica 0.1.0 with import deduplication support:

1. Nixica migration: Replaced flake-parts + import-tree with nixica.lib.mkFlake inputs ./nix
2. Dev partition: Added dev/flake.nix and nix/dev.nix using mkPartitionModule with omnix, cachix, and flake CI modules
3. Import deduplication: Implemented importAndPublish pattern with flakeModules.flakeModules for proper dedup
4. Test restructuring: Renamed test/import-deduplicate/ → test/modules/flake/werrorwolf/it-import-deduplicates/ per convention
5. Test flake: Uses nixica.lib.mkFlake with nixica.follows = "werrorwolf/nixica"
6. CI: Updated .gitlab-ci.yml to gitlab-ci 0.19.0 remote template with omnix + cachix + flake modules

Changes

• flake.nix: nixica 0.1.0, gitlab-ci 0.19.0, nixpkgs 25.11 (strict refs)
• nix/: import-tree conventions (local:/_local: patterns)
• dev/: dev partition with CI config (omnix, cachix, flake validation)
• test/modules/flake/werrorwolf/it-import-deduplicates/: restructured test with nixica follows

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