Fix Nix build by removing accidentally committed build artifacts

- Remove server/_build/ and server/deps/ from git tracking
- Update .gitignore to properly ignore server build directories
- These directories caused symlink conflicts in Nix build

🤖 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

@@ -1,10 +0,0 @@
-{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',[]}}]}.

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

@@ -1,26 +0,0 @@
-{application,jason,
-             [{modules,['Elixir.Enumerable.Jason.OrderedObject',
-                        'Elixir.Jason','Elixir.Jason.Codegen',
-                        'Elixir.Jason.DecodeError','Elixir.Jason.Decoder',
-                        'Elixir.Jason.Decoder.Unescape','Elixir.Jason.Encode',
-                        'Elixir.Jason.EncodeError','Elixir.Jason.Encoder',
-                        'Elixir.Jason.Encoder.Any',
-                        'Elixir.Jason.Encoder.Atom',
-                        'Elixir.Jason.Encoder.BitString',
-                        'Elixir.Jason.Encoder.Date',
-                        'Elixir.Jason.Encoder.DateTime',
-                        'Elixir.Jason.Encoder.Float',
-                        'Elixir.Jason.Encoder.Integer',
-                        'Elixir.Jason.Encoder.Jason.Fragment',
-                        'Elixir.Jason.Encoder.Jason.OrderedObject',
-                        'Elixir.Jason.Encoder.List',
-                        'Elixir.Jason.Encoder.Map',
-                        'Elixir.Jason.Encoder.NaiveDateTime',
-                        'Elixir.Jason.Encoder.Time','Elixir.Jason.Formatter',
-                        'Elixir.Jason.Fragment','Elixir.Jason.Helpers',
-                        'Elixir.Jason.OrderedObject','Elixir.Jason.Sigil']},
-              {optional_applications,[decimal]},
-              {applications,[kernel,stdlib,elixir,decimal]},
-              {description,"A blazing fast JSON parser and generator in pure Elixir.\n"},
-              {registered,[]},
-              {vsn,"1.4.4"}]}.

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

@@ -1,9 +0,0 @@
-{application,systant,
-             [{modules,['Elixir.Systant','Elixir.Systant.Application',
-                        'Elixir.Systant.MqttClient']},
-              {optional_applications,[]},
-              {applications,[kernel,stdlib,elixir,logger,tortoise,jason]},
-              {description,"systant"},
-              {registered,[]},
-              {vsn,"0.1.0"},
-              {mod,{'Elixir.Systant.Application',[]}}]}.