feat: Add --all flag to estimate command to list available configs

- Added find_configs_directory() to use same logic as API (api/configs_repo/official first, then configs/)
- Added list_all_configs() to display all 24 configs grouped by category with descriptions
- Updated CLI to support --all flag, making config argument optional when --all is used
- Added 2 new tests for --all flag functionality
- All 51 tests passing (51 passed, 1 skipped)

This enables users to discover all available preset configs without checking the API or filesystem directly.

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

src/skill_seekers/cli/main.py

@@ -176,7 +176,8 @@ For more information: https://github.com/yusufkaraaslan/Skill_Seekers
         help="Estimate page count before scraping",
         description="Estimate total pages for documentation scraping"
     )
-    estimate_parser.add_argument("config", help="Config JSON file")
+    estimate_parser.add_argument("config", nargs="?", help="Config JSON file")
+    estimate_parser.add_argument("--all", action="store_true", help="List all available configs")
     estimate_parser.add_argument("--max-discovery", type=int, help="Max pages to discover")
 
     # === extract-test-examples subcommand ===
@@ -411,7 +412,11 @@ def main(argv: Optional[List[str]] = None) -> int:
 
         elif args.command == "estimate":
             from skill_seekers.cli.estimate_pages import main as estimate_main
-            sys.argv = ["estimate_pages.py", args.config]
+            sys.argv = ["estimate_pages.py"]
+            if args.all:
+                sys.argv.append("--all")
+            elif args.config:
+                sys.argv.append(args.config)
             if args.max_discovery:
                 sys.argv.extend(["--max-discovery", str(args.max_discovery)])
             return estimate_main() or 0