refactor: migrate to directory-based stack structure

- Updated ComposeService to run docker commands from stack-specific directories, ensuring relative paths resolve correctly.
- Refactored FileSystemService to manage stacks as directories, including methods for creating, updating, and deleting stacks.
- Implemented automatic migration of existing flat-file stacks to the new directory structure on server startup.
- Adjusted API routes to use stack names instead of filenames, simplifying stack management.
- Modified frontend components to align with the new stack naming conventions and removed unnecessary file extensions.

frontend/src/components/HomeDashboard.tsx

@@ -104,17 +104,18 @@ export default function HomeDashboard() {
 
   const handleCreateStack = async () => {
     if (!newStackName.trim() || !convertedYaml) return;
-    const filename = newStackName.endsWith('.yml') ? newStackName : newStackName + '.yml';
+    // Send stackName directly (no .yml extension - backend creates directory)
+    const stackName = newStackName.trim();
     try {
       // Create the stack
       const createResponse = await apiFetch('/stacks', {
         method: 'POST',
-        body: JSON.stringify({ filename }),
+        body: JSON.stringify({ stackName }),
       });
       if (!createResponse.ok) throw new Error('Failed to create stack');
 
       // Save the converted YAML content
-      const saveResponse = await apiFetch(`/stacks/${filename}`, {
+      const saveResponse = await apiFetch(`/stacks/${stackName}`, {
         method: 'PUT',
         body: JSON.stringify({ content: convertedYaml }),
       });