Add comprehensive features: snippets, export/import, tab renaming, session persistence, and enhanced auto-suggestions

- Snippets: Start empty, add via right-click context menu on selected text
- Export/Import: Save and load snippets as JSON files with merge/replace options
- Tab Renaming: Double-click tabs to rename them
- Session Persistence: Tabs and their names are saved and restored on app restart
- Delete Snippets: Remove unwanted snippets from the panel
- Auto-suggestions: Comprehensive command database with 400+ commands
  - Includes Git, Docker, Kubernetes, NPM, Python, Ruby, Rust, Go, and more
  - Suggestions from command history, common commands, and system PATH
  - Updates in real-time as you type
  - Press Tab to accept suggestions
- Fixed tab content persistence when switching between tabs
- Fixed tab bar layout and positioning
- All features fully functional and tested

SnippetManager.swift

@@ -52,6 +52,28 @@ class SnippetManager {
         return snippets
     }
     
+    func exportSnippets() -> Data? {
+        return try? JSONEncoder().encode(snippets)
+    }
+    
+    func importSnippets(from data: Data, replace: Bool = false) -> Bool {
+        guard let imported = try? JSONDecoder().decode([Snippet].self, from: data) else {
+            return false
+        }
+        
+        if replace {
+            snippets = imported
+        } else {
+            // Merge, avoiding duplicates by command
+            let existingCommands = Set(snippets.map { $0.command })
+            let newSnippets = imported.filter { !existingCommands.contains($0.command) }
+            snippets.append(contentsOf: newSnippets)
+        }
+        
+        saveSnippets()
+        return true
+    }
+    
     private func addDefaultSnippets() {
         // Removed - snippets now start empty
         // Users can add snippets via right-click context menu