Restructure as monorepo and add flake packages/apps

- Move Elixir code to server/ subdirectory for monorepo structure
- Update flake.nix to provide packages and apps outputs for nix run support
- Update nix/package.nix to accept src parameter instead of fetchgit
- Add NixOS module export for easy consumption

Now supports: nix run, nix build, and nix develop from git repo

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

server/_build/dev/lib/gen_state_machine/ebin/gen_state_machine.app

@@ -0,0 +1,10 @@
+{application,gen_state_machine,
+             [{modules,['Elixir.GenStateMachine',
+                        'Elixir.GenStateMachine.Application',
+                        'Elixir.GenStateMachine.Translator']},
+              {optional_applications,[]},
+              {applications,[kernel,stdlib,elixir,logger]},
+              {description,"An Elixir wrapper for gen_statem."},
+              {registered,[]},
+              {vsn,"3.0.0"},
+              {mod,{'Elixir.GenStateMachine.Application',[]}}]}.