feat: add --scan-mode CLI option with quick/standard/deep modes

Introduces scan mode selection to control testing depth and methodology:
- quick: optimized for CI/CD, focuses on recent changes and high-impact vulns
- standard: balanced coverage with systematic methodology
- deep: exhaustive testing with hierarchical agent swarm (now default)

Each mode has dedicated prompt modules with detailed pentesting guidelines
covering reconnaissance, mapping, business logic analysis, exploitation,
and vulnerability chaining strategies.

Closes #152

strix/interface/cli.py

@@ -66,6 +66,8 @@ async def run_cli(args: Any) -> None:  # noqa: PLR0915
     console.print(startup_panel)
     console.print()
 
+    scan_mode = getattr(args, "scan_mode", "deep")
+
     scan_config = {
         "scan_id": args.run_name,
         "targets": args.targets_info,
@@ -73,7 +75,7 @@ async def run_cli(args: Any) -> None:  # noqa: PLR0915
         "run_name": args.run_name,
     }
 
-    llm_config = LLMConfig()
+    llm_config = LLMConfig(scan_mode=scan_mode)
     agent_config = {
         "llm_config": llm_config,
         "max_iterations": 300,