fix: handle etcd watcher creation errors gracefully

The pods were crashing with a MatchError when the etcd watcher failed
to initialize. The code was pattern matching on {:ok, watcher} but
eetcd was returning {:error, :eetcd_conn_unavailable}.

Error:
  ** (MatchError) no match of right hand side value:
  {:error, :eetcd_conn_unavailable}

This was causing CrashLoopBackOff because the application couldn't
start the Monitoring.Supervisor due to EtcdCoordinator initialization
failure.

Fix:
  - Add case statement to handle both {:ok, watcher} and {:error, reason}
  - Log the specific error when watcher creation fails
  - Return proper error tuple to supervisor for clean shutdown

lib/towerops/monitoring/etcd_coordinator.ex

@@ -38,16 +38,23 @@ defmodule Towerops.Monitoring.EtcdCoordinator do
         watch_ctx = :eetcd_watch.new()
         watch_with_key = :eetcd_watch.with_key(watch_ctx, "towerops/locks/")
         watch_with_prefix = :eetcd_watch.with_prefix(watch_with_key)
-        {:ok, watcher} = :eetcd_watch.watch(conn, watch_with_prefix)
-        Logger.info("Watching etcd for lock releases")
 
-        # Start acquiring locks for all devices
-        send(self(), :acquire_locks)
+        case :eetcd_watch.watch(conn, watch_with_prefix) do
+          {:ok, watcher} ->
+            Logger.info("Watching etcd for lock releases")
 
-        # Schedule periodic rebalancing (safety net for missed watch events)
-        schedule_rebalance()
+            # Start acquiring locks for all devices
+            send(self(), :acquire_locks)
 
-        {:ok, %{conn: conn, watcher: watcher, owned_leases: %{}}}
+            # Schedule periodic rebalancing (safety net for missed watch events)
+            schedule_rebalance()
+
+            {:ok, %{conn: conn, watcher: watcher, owned_leases: %{}}}
+
+          {:error, reason} ->
+            Logger.error("Failed to create etcd watcher: #{inspect(reason)}")
+            {:stop, {:etcd_watcher_failed, reason}}
+        end
 
       {:error, reason} ->
         Logger.error("Failed to connect to etcd: #{inspect(reason)}")