feat: add comment field to shared environment variables

Add comment field support to the "New Shared Variable" modal, ensuring it's saved properly for both normal and shared environment variables at all levels (Team, Project, Environment).

Changes:
- Add comment property, validation, and dispatch to Add component (Livewire & view)
- Update saveKey methods in Team, Project, and Environment to accept comment
- Replace SharedEnvironmentVariable model's $guarded with explicit $fillable array
- Include comment field in creation flow for all shared variable types

The comment field (max 256 chars, optional) is now available when creating shared variables and is consistently saved across all variable types.

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

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

app/Models/SharedEnvironmentVariable.php

@@ -6,7 +6,23 @@ use Illuminate\Database\Eloquent\Model;
 
 class SharedEnvironmentVariable extends Model
 {
-    protected $guarded = [];
+    protected $fillable = [
+        // Core identification
+        'key',
+        'value',
+        'comment',
+
+        // Type and relationships
+        'type',
+        'team_id',
+        'project_id',
+        'environment_id',
+
+        // Boolean flags
+        'is_multiline',
+        'is_literal',
+        'is_shown_once',
+    ];
 
     protected $casts = [
         'key' => 'string',