Add service infrastructure for long-running deployment

- Add configuration system (config/*.exs, OrgGarden.Config)
- Refactor supervision tree with DynamicSupervisor and Registry
- Add OrgGarden.Server for serve mode lifecycle management
- Add health check HTTP endpoints (Bandit/Plug on :9090)
- Add telemetry events for export and watcher operations
- Implement graceful shutdown with SIGTERM handling
- Add Mix Release support with overlay scripts
- Add NixOS module for systemd service deployment
- Update documentation with service usage

rel/env.sh.eex

@@ -0,0 +1,16 @@
+#!/bin/sh
+
+# Release environment configuration
+# This file is evaluated before the release starts
+
+# Disable Erlang distribution (not needed for this application)
+export RELEASE_DISTRIBUTION=none
+
+# Enable shell history in IEx
+export ERL_AFLAGS="-kernel shell_history enabled"
+
+# Set release node name
+export RELEASE_NODE=org_garden
+
+# Log to console by default
+export ELIXIR_ERL_OPTIONS="-noshell"