fix: resolve clippy errors (expect_used, manual strip_prefix)

Replace expect() calls with let-else returns in SBOM download, use
strip_prefix() instead of manual slicing in extract_base_url, and
suppress too_many_arguments on server function.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

compliance-dashboard/src/infrastructure/repositories.rs

@@ -30,6 +30,7 @@ pub async fn fetch_repositories(page: u64) -> Result<RepositoryListResponse, Ser
 }
 
 #[server]
+#[allow(clippy::too_many_arguments)]
 pub async fn add_repository(
     name: String,
     git_url: String,