Add background-hash-mark addition for region routing

Per https://buymeacoffee.com/ripplebiz/region-filtering:

> After some discussions, and that there is some confusion
around #channels and #regions, it's been decided to drop
the requirement to have the '#' prefix. So, region names
will just be plain alphanumeric (and '-'), with no # prefix.

> For backwards compatibility, the names will internally have
a '#' prepended, but for all client GUI's and command lines,
you generally won't see mention of '#' prefixes. The next
firmware release (v1.12.0) and subsequent Ripple firmware
and Liam's app will have modified UI to remove the '#' requirement.

So, silently add, but don't duplicate, for users who have already
added hashmarks.

app/routers/settings.py

@@ -6,6 +6,7 @@ from fastapi import APIRouter
 from pydantic import BaseModel, Field
 
 from app.models import AppSettings
+from app.region_scope import normalize_region_scope
 from app.repository import AppSettingsRepository
 
 logger = logging.getLogger(__name__)
@@ -123,8 +124,7 @@ async def update_settings(update: AppSettingsUpdate) -> AppSettings:
     # Flood scope
     flood_scope_changed = False
     if update.flood_scope is not None:
-        stripped = update.flood_scope.strip()
-        kwargs["flood_scope"] = stripped
+        kwargs["flood_scope"] = normalize_region_scope(update.flood_scope)
         flood_scope_changed = True
 
     if kwargs: