fix: Show available variables in triple-quote format in AI prompt

The AI follows the pattern better when the available variables are
shown in the exact format they should be used:
  """{input}""", """{response}""", etc.

This helps the AI generate code that properly uses triple quotes
for variable substitution.

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

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

src/smarttools/ui_urwid.py

@@ -1829,12 +1829,13 @@ class SmartToolsUI:
         ai_provider_select_btn = Button3DCompact("▼", on_press=show_ai_provider_dropdown)
 
         # Default prompt template for AI code generation/adjustment
+        # Show variables in triple-quote format so the AI follows the pattern
+        vars_formatted = ', '.join(f'\"\"\"{{{v}}}\"\"\"' for v in vars_available)
         default_ai_prompt = f"""Write inline Python code (NOT a function definition) according to my instruction.
 
-The code runs directly with variable substitution. To use an available variable:
-- Wrap the variable name in curly braces: {{variable}}
-- Use triple quotes since the substituted content may contain quotes/newlines
-- Example: my_var = \"\"\"{{response}}\"\"\"
+The code runs directly with variable substitution. Any available variable used must be wrapped in triple quotes and curly braces like this: \"\"\"{{variable}}\"\"\". The triple quotes are needed since the substituted content may contain quotes/newlines.
+
+Example: my_var = \"\"\"{{response}}\"\"\"
 
 INSTRUCTION: [Describe what you want]
 
@@ -1843,7 +1844,7 @@ CURRENT CODE:
 {{code}}
 ```
 
-AVAILABLE VARIABLES: {', '.join(vars_available)}
+AVAILABLE VARIABLES: {vars_formatted}
 
 IMPORTANT: Return ONLY executable inline code. Do NOT wrap in a function.
 No explanations, no markdown fencing, just the code."""