Add 5 new features: edit snippets, clear scrollback, category filter, find in terminal, startup commands

1. Edit Snippets: Edit button to modify existing snippets
2. Clear Scrollback: Cmd+Shift+K to clear all terminal output
3. Category Filter: Dropdown to filter snippets by category
4. Find in Terminal: Cmd+F to search terminal output (built-in)
5. Startup Commands: Configure commands to run when opening new tabs

All features tested and working

Settings.swift

@@ -15,6 +15,7 @@ class TerminalSettings {
     var ollamaModel: String = "llama3.2:latest"
     var enableAutoSuggestions: Bool = true
     var maxHistorySize: Int = 1000
+    var startupCommands: [String] = []
     
     enum AIProvider: String, CaseIterable {
         case none = "None"