Switch to cases/{new,in-progress,completed}/ directory structure

Replace single CASES_DIR with find_case_dir() that searches across
all status directories. New cases created in cases/new/{number}/.

Config: CASES_BASE, CASES_NEW, CASES_IN_PROGRESS, CASES_COMPLETED
Docker: added -v /home/chaim/legal-ai/cases:/cases volume mount

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

mcp-server/src/legal_mcp/services/docx_exporter.py

@@ -171,7 +171,7 @@ async def export_decision(case_id: UUID, output_path: str | None = None) -> str:
 
     # Determine output path
     if not output_path:
-        case_dir = config.CASES_DIR / case["case_number"] / "output"
+        case_dir = config.find_case_dir(case["case_number"]) / "output"
         case_dir.mkdir(parents=True, exist_ok=True)
         output_path = str(case_dir / f"החלטה-{case['case_number']}.docx")