Rename sessions to _sessions, drop legacy migrations table

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

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

app/RSpade/Core/Session/Session.php

@@ -101,7 +101,7 @@ class Session extends Rsx_System_Model_Abstract
      * The table associated with the model
      * @var string
      */
-    protected $table = 'sessions';
+    protected $table = '_sessions';
 
     /**
      * The attributes that should be cast

app/RSpade/Core/Session/Session_Cleanup_Service.php

@@ -36,7 +36,7 @@ class Session_Cleanup_Service extends Rsx_Service_Abstract
     {
         // Logged-in sessions: older than 365 days
         $logged_in_cutoff = now()->subDays(365);
-        $logged_in_deleted = DB::table('sessions')
+        $logged_in_deleted = DB::table('_sessions')
             ->whereNotNull('login_user_id')
             ->where('last_active', '<', $logged_in_cutoff)
             ->delete();
@@ -45,7 +45,7 @@ class Session_Cleanup_Service extends Rsx_Service_Abstract
 
         // Anonymous sessions: older than 14 days
         $anonymous_cutoff = now()->subDays(14);
-        $anonymous_deleted = DB::table('sessions')
+        $anonymous_deleted = DB::table('_sessions')
             ->whereNull('login_user_id')
             ->where('last_active', '<', $anonymous_cutoff)
             ->delete();