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/modules/utils/email/config/binds.conf

@@ -0,0 +1,129 @@
+# Binds are of the form <key sequence> = <command to run>
+# To use '=' in a key sequence, substitute it with "Eq": "<Ctrl+Eq>"
+# If you wish to bind #, you can wrap the key sequence in quotes: "#" = quit
+<C-p> = :prev-tab<Enter>
+<C-n> = :next-tab<Enter>
+<C-t> = :term<Enter>
+? = :help keys<Enter>
+
+[messages]
+q = :quit<Enter>
+
+j = :next<Enter>
+<Down> = :next<Enter>
+<C-d> = :next 50%<Enter>
+<C-f> = :next 100%<Enter>
+<PgDn> = :next 100%<Enter>
+
+k = :prev<Enter>
+<Up> = :prev<Enter>
+<C-u> = :prev 50%<Enter>
+<C-b> = :prev 100%<Enter>
+<PgUp> = :prev 100%<Enter>
+g = :select 0<Enter>
+G = :select -1<Enter>
+
+J = :next-folder<Enter>
+K = :prev-folder<Enter>
+H = :collapse-folder<Enter>
+L = :expand-folder<Enter>
+
+v = :mark -t<Enter>
+V = :mark -v<Enter>
+
+T = :toggle-threads<Enter>
+
+<Enter> = :view<Enter>
+d = :prompt 'Really delete this message?' 'delete-message'<Enter>
+D = :delete<Enter>
+A = :archive flat<Enter>
+
+C = :compose<Enter>
+
+rr = :reply -a<Enter>
+rq = :reply -aq<Enter>
+Rr = :reply<Enter>
+Rq = :reply -q<Enter>
+
+c = :cf<space>
+$ = :term<space>
+! = :term<space>
+| = :pipe<space>
+
+/ = :search<space>
+\ = :filter<space>
+n = :next-result<Enter>
+N = :prev-result<Enter>
+<Esc> = :clear<Enter>
+
+[messages:folder=Drafts]
+<Enter> = :recall<Enter>
+
+[view]
+/ = :toggle-key-passthrough<Enter>/
+q = :close<Enter>
+O = :open<Enter>
+S = :save<space>
+| = :pipe<space>
+D = :delete<Enter>
+A = :archive flat<Enter>
+
+<C-l> = :open-link <space>
+
+f = :forward<Enter>
+rr = :reply -a<Enter>
+rq = :reply -aq<Enter>
+Rr = :reply<Enter>
+Rq = :reply -q<Enter>
+
+H = :toggle-headers<Enter>
+<C-k> = :prev-part<Enter>
+<C-j> = :next-part<Enter>
+J = :next<Enter>
+K = :prev<Enter>
+
+[view::passthrough]
+$noinherit = true
+$ex = <C-x>
+<Esc> = :toggle-key-passthrough<Enter>
+
+[compose]
+# Keybindings used when the embedded terminal is not selected in the compose
+# view
+$noinherit = true
+$ex = <C-x>
+<C-k> = :prev-field<Enter>
+<C-j> = :next-field<Enter>
+<A-p> = :switch-account -p<Enter>
+<A-n> = :switch-account -n<Enter>
+<tab> = :next-field<Enter>
+<backtab> = :prev-field<Enter>
+<C-p> = :prev-tab<Enter>
+<C-n> = :next-tab<Enter>
+
+[compose::editor]
+# Keybindings used when the embedded terminal is selected in the compose view
+$noinherit = true
+$ex = <C-x>
+<C-k> = :prev-field<Enter>
+<C-j> = :next-field<Enter>
+<C-p> = :prev-tab<Enter>
+<C-n> = :next-tab<Enter>
+
+[compose::review]
+# Keybindings used when reviewing a message to be sent
+y = :send<Enter>
+n = :abort<Enter>
+v = :preview<Enter>
+p = :postpone<Enter>
+q = :choose -o d discard abort -o p postpone postpone<Enter>
+e = :edit<Enter>
+a = :attach<space>
+d = :detach<space>
+
+[terminal]
+$noinherit = true
+$ex = <C-x>
+
+<C-p> = :prev-tab<Enter>
+<C-n> = :next-tab<Enter>