feat(tui): enhance system prompt with workspace structure information

apps/infrastructure/src/utils.rs

@@ -149,3 +149,45 @@ pub fn write_osc52(output: &mut impl Write, text: &str) -> std::io::Result<()> {
     output.flush()?;
     Ok(())
 }
+
+// ---------------------------------------------------------------------------
+// Workspace Tree Builder
+// ---------------------------------------------------------------------------
+
+/// Build a string representing the directory tree of `root`, up to `max_files` limits.
+/// Automatically respects `.gitignore` and `.ignore` via the `ignore` crate.
+pub fn build_workspace_tree(root: &Path, max_files: usize) -> String {
+    use ignore::WalkBuilder;
+    let mut tree = String::new();
+    let mut count = 0;
+    
+    // hidden(false) allows files like .github to be seen, but it still respects .gitignore
+    // and ignores .git directories by default.
+    for result in WalkBuilder::new(root).hidden(false).build() {
+        if let Ok(entry) = result {
+            if count >= max_files {
+                tree.push_str("\n... (truncated)");
+                break;
+            }
+            
+            let path = entry.path();
+            if let Ok(rel) = path.strip_prefix(root) {
+                let name = rel.to_string_lossy();
+                if name.is_empty() {
+                    tree.push_str(".\n");
+                } else {
+                    let depth = entry.depth();
+                    let indent = "  ".repeat(depth.saturating_sub(1));
+                    let is_dir = entry.file_type().map(|ft| ft.is_dir()).unwrap_or(false);
+                    let suffix = if is_dir { "/" } else { "" };
+                    
+                    let filename = entry.file_name().to_string_lossy();
+                    tree.push_str(&format!("{indent}{filename}{suffix}\n"));
+                    count += 1;
+                }
+            }
+        }
+    }
+    
+    tree.trim_end().to_string()
+}