feat: respect NO_COLOR env var and TERM=dumb (#4079)

Add should_use_color() function to hermes_cli/colors.py that checks
NO_COLOR (https://no-color.org/) and TERM=dumb before emitting ANSI
escapes. The existing color() helper now uses this function instead
of a bare isatty() check.

This is the foundation — cli.py and banner.py still have inline ANSI
constants that bypass this module (tracked in #4071).

Closes #4066

Co-authored-by: SHL0MS <SHL0MS@users.noreply.github.com>

hermes_cli/colors.py

@@ -1,8 +1,24 @@
 """Shared ANSI color utilities for Hermes CLI modules."""
 
+import os
 import sys
 
 
+def should_use_color() -> bool:
+    """Return True when colored output is appropriate.
+
+    Respects the NO_COLOR environment variable (https://no-color.org/)
+    and TERM=dumb, in addition to the existing TTY check.
+    """
+    if os.environ.get("NO_COLOR") is not None:
+        return False
+    if os.environ.get("TERM") == "dumb":
+        return False
+    if not sys.stdout.isatty():
+        return False
+    return True
+
+
 class Colors:
     RESET = "\033[0m"
     BOLD = "\033[1m"
@@ -16,7 +32,7 @@ class Colors:
 
 
 def color(text: str, *codes) -> str:
-    """Apply color codes to text (only when output is a TTY)."""
+    """Apply color codes to text (only when color output is appropriate)."""
-    if not sys.stdout.isatty():
+    if not should_use_color():
         return text
     return "".join(codes) + text + Colors.RESET