refactor: reorganize flake structure and consolidate user config

Directory structure:
- Move from src/ to root level (system/, user/)
- Remove unused machines (workstation, vm, laptop)

User configuration:
- Add user/home.nix for shared defaults (pass, essentials, default modules)
- Centralize user options in user/default.nix
- Move submodules to consistent paths (bash/bash, git/git, neovim/nvim, vim/vim)

Module reorganization:
- Flatten nested module structures (remove /modules/ subdirs)
- Split CLI vs GUI tools (dev/ for CLI, gui/dev/ for GUI)
- Move neovim/vim to top-level modules (not under utils/)
- Remove security.enable - pass now in user/home.nix
- Remove utils.enable - essentials now in user/home.nix
- Add security/yubikey module with yubikey-manager, age-plugin-yubikey
- Move pcb, design to gui/dev/
- Replace penpot docker wrapper with nixpkgs penpot-desktop
- Remove i3 config
- Remove deprecated wsl.nativeSystemd option

GUI improvements:
- Browser-focused mimeApps in gui/default.nix
- Each WM handles its own auto-start via profileExtra

Cleanup:
- Update README with new structure
- Update justfile paths and valid systems
- Fix submodule paths in .gitmodules

user/keys/ssh/README.md

@@ -0,0 +1,5 @@
+# SSH Keys
+
+yubikey.pub.key -> PGP derived from `pgp.yubikey.pub.key`
+work.pub.key - ?
+graphone.pub.key -> For Android `pass`

user/keys/ssh/graphone.pub.key

@@ -0,0 +1 @@
+ecdsa-sha2-nistp256 AAAAE2VjZHNhLXNoYTItbmlzdHAyNTYAAAAIbmlzdHAyNTYAAABBBJM1HutPcWXdeTaAXY7ha8SlgeZFtLJGwNa3Kd/DL/R38fq5+fkh3iCoHgv+iiKcordtVTMhbOsHhz3H+Jm274c=

user/keys/ssh/work.pub.key

@@ -0,0 +1 @@
+ssh-rsa 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

user/keys/ssh/yubikey.pub.key

@@ -0,0 +1 @@
+ssh-rsa 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