treewide: use StaticFiles() rather than rel path

This commit is not exhaustive, and it is a trend in this codebase to not
use StaticFiles() and instead use relative paths. This means the code
cannot run anywhere other than the source code directory, as it will not
find the files it is looking for

lnbits/__main__.py

@@ -5,7 +5,7 @@ from starlette.requests import Request
 
 from loguru import logger
 
-from .commands import bundle_vendored, migrate_databases, transpile_scss
+from .commands import migrate_databases
 from .settings import (
     DEBUG,
     LNBITS_COMMIT,
@@ -21,8 +21,6 @@ from .settings import (
 uvloop.install()
 
 asyncio.create_task(migrate_databases())
-transpile_scss()
-bundle_vendored()
 
 from .app import create_app