Add comprehensive documentation for DMARQ, including user guides, deployment instructions, and feature descriptions

- Created main documentation index and user guide with sections on getting started, dashboard overview, managing domains, and reports.
- Added detailed deployment guide for Docker and manual installation.
- Included user-friendly explanations of DMARC, its benefits, and how to manage domains and reports.
- Implemented visual assets for dashboard, domains, IMAP, and reports.
- Established requirements for documentation build using MkDocs and Material theme.
- Integrated navigation structure for easy access to all documentation sections.

backend/app/api/api_v1/api.py

@@ -1,6 +1,6 @@
 from fastapi import APIRouter
 
-from app.api.api_v1.endpoints import domains, health, reports, setup, imap
+from app.api.api_v1.endpoints import domains, health, reports, setup, imap, stats
 
 api_router = APIRouter()
 
@@ -9,4 +9,5 @@ api_router.include_router(health.router, tags=["health"])
 api_router.include_router(domains.router, prefix="/domains", tags=["domains"])
 api_router.include_router(reports.router, prefix="/reports", tags=["reports"])
 api_router.include_router(setup.router, prefix="/setup", tags=["setup"])
-api_router.include_router(imap.router, prefix="/imap", tags=["imap"])
+api_router.include_router(imap.router, prefix="/imap", tags=["imap"])
+api_router.include_router(stats.router, prefix="/stats", tags=["stats"])