feat(ai_review): fmt_tokens() humanizes token counts

pilot/ai_review.py

@@ -141,6 +141,26 @@ def truncate_diff(text: str, max_chars: int) -> tuple[str, bool, int]:
     return text[:max_chars] + f"\n\n[diff truncated at {max_chars} characters]\n", True, orig_len
 
 
+def fmt_tokens(n) -> str:
+    """1234567 -> '1,234,567 (1.2M)'; 0 -> '0'; <1000 -> comma-only; None/negative -> '?'.
+
+    Always returns the full comma-separated number; the short suffix is a
+    parenthetical for fast scanning. Caps at B; the cost model never exceeds M.
+    """
+    if n is None:
+        return "?"
+    if not isinstance(n, (int, float)) or n < 0:
+        return "?"
+    n = int(n)
+    if n < 1000:
+        return f"{n:,}"
+    if n < 1_000_000:
+        return f"{n:,} ({n / 1000:.1f}K)"
+    if n < 1_000_000_000:
+        return f"{n:,} ({n / 1_000_000:.1f}M)"
+    return f"{n:,} ({n / 1_000_000_000:.1f}B)"
+
+
 def parse_text_blocks(content: list) -> str:
     """Join `type:"text"` blocks from an Anthropic /v1/messages response.