Improve tool output formatting

1. str_replace: Show insertion/deletion counts with colors
   "✅ +N insertions | -M deletions" (green/red)

2. write_file: Compact format with human-readable sizes
   "✅ wrote N lines | Xk chars"

3. read_file: Cleaner format
   "🔍 N lines read" instead of "📄 File content (N lines)"

4. webdriver_quit: Show correct driver name (safaridriver vs chromedriver)

5. read_file: When start position exceeds file length, read last 100 chars
   with explanation instead of failing

6. shell: Remove redundant "Command failed:" prefix from error messages

crates/g3-core/src/tools/shell.rs

@@ -61,7 +61,7 @@ pub async fn execute_shell<W: UiWriter>(tool_call: &ToolCall, ctx: &ToolContext<
                     result.stdout.trim().to_string()
                 })
             } else {
-                Ok(format!("❌ Command failed: {}", result.stderr.trim()))
+                Ok(format!("❌ {}", result.stderr.trim()))
             }
         }
         Err(e) => Ok(format!("❌ Execution error: {}", e)),