Add clear cache indicators to output

- Show "⚡ CACHED RESULTS (Xh old)" in compact output header
- Add "use --refresh for fresh data" hint
- Track from_cache and cache_age_hours in Report schema
- Update UI to show cache age in stderr message

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

scripts/lib/ui.py

@@ -177,8 +177,12 @@ class ProgressDisplay:
         sys.stderr.write(f"{Colors.CYAN}X:{Colors.RESET} {x_count} posts\n\n")
         sys.stderr.flush()
 
-    def show_cached(self):
-        sys.stderr.write(f"{Colors.GREEN}⚡{Colors.RESET} {Colors.DIM}Using cached results{Colors.RESET}\n\n")
+    def show_cached(self, age_hours: float = None):
+        if age_hours is not None:
+            age_str = f" ({age_hours:.1f}h old)"
+        else:
+            age_str = ""
+        sys.stderr.write(f"{Colors.GREEN}⚡{Colors.RESET} {Colors.DIM}Using cached results{age_str} - use --refresh for fresh data{Colors.RESET}\n\n")
         sys.stderr.flush()
 
     def show_error(self, message: str):