fix(ui): quiet HN and YouTube spinners in non-TTY mode

Reddit and X are the star of the show. In Claude Code (non-TTY),
suppress ⏳ start messages for HN and YouTube so Reddit/X are the
first visible lines. HN/YouTube still show ✓ completion messages.
Also suppress [HN] debug logs in non-TTY to reduce output clutter.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

scripts/lib/hackernews.py

@@ -31,9 +31,10 @@ ENRICH_LIMITS = {
 
 
 def _log(msg: str):
-    """Log to stderr."""
-    sys.stderr.write(f"[HN] {msg}\n")
-    sys.stderr.flush()
+    """Log to stderr (only in TTY mode to avoid cluttering Claude Code output)."""
+    if sys.stderr.isatty():
+        sys.stderr.write(f"[HN] {msg}\n")
+        sys.stderr.flush()
 
 
 def _date_to_unix(date_str: str) -> int: