Remove ANSI formatting codes from g3-core

Move terminal formatting responsibility to g3-cli layer:

- format_str_replace_summary(): Remove ANSI codes, add colorize_str_replace_summary()
  helper in CLI to apply green/red colors for insertions/deletions
- format_timing_footer(): Remove dimming ANSI codes (now plain text)
- str_replace tool result: Remove ANSI codes from success message

Remaining acceptable ANSI usage in g3-core:
- iTerm2 inline image protocol (terminal-specific escape sequence)
- Image metadata dimming (direct print, would need larger refactor)
- Terminal beep for stale TODO warning (audio, not visual)
- ANSI stripping utility in research.rs (not output)

This continues the separation of concerns: g3-core handles logic,
g3-cli handles all terminal formatting.

crates/g3-core/src/streaming.rs

@@ -142,11 +142,11 @@ pub fn format_timing_footer(
     // Add token usage info if available (dimmed)
     if let Some(tokens) = turn_tokens {
         format!(
-            "{}  \x1b[2m{} ◉ | {:.0}%\x1b[0m",
+            "{}  {} ◉ | {:.0}%",
             timing, tokens, context_percentage
         )
     } else {
-        format!("{}  \x1b[2m{:.0}%\x1b[0m", timing, context_percentage)
+        format!("{}  {:.0}%", timing, context_percentage)
     }
 }
 
@@ -326,11 +326,11 @@ pub fn format_write_file_result(tool_result: &str) -> String {
 /// Format a str_replace result summary.
 pub fn format_str_replace_summary(insertions: i32, deletions: i32) -> String {
     if insertions > 0 && deletions > 0 {
-        format!("\x1b[32m+{}\x1b[0m \x1b[2m|\x1b[0m \x1b[31m-{}\x1b[0m", insertions, deletions)
+        format!("+{} | -{}", insertions, deletions)
     } else if insertions > 0 {
-        format!("\x1b[32m+{}\x1b[0m", insertions)
+        format!("+{}", insertions)
     } else {
-        format!("\x1b[31m-{}\x1b[0m", deletions)
+        format!("-{}", deletions)
     }
 }
 

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

@@ -582,7 +582,7 @@ pub async fn execute_str_replace<W: UiWriter>(
 
     // Write the result back to the file
     match std::fs::write(&file_path, &result) {
-        Ok(()) => Ok(format!("✅ \x1b[32m+{} insertions\x1b[0m | \x1b[31m-{} deletions\x1b[0m", insertions, deletions)),
+        Ok(()) => Ok(format!("✅ +{} insertions | -{} deletions", insertions, deletions)),
         Err(e) => Ok(format!("❌ Failed to write to file '{}': {}", file_path, e)),
     }
 }