s3tables: fix shared table-location bucket mapping collisions (#8286)

* s3tables: prevent shared table-location bucket mapping overwrite

* Update weed/s3api/bucket_paths.go

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

---------

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

weed/s3api/bucket_paths_test.go

@@ -0,0 +1,45 @@
+package s3api
+
+import "testing"
+
+func TestNormalizeTableLocationMappingPath(t *testing.T) {
+	testCases := []struct {
+		name string
+		raw  string
+		want string
+	}{
+		{
+			name: "legacy table path maps to bucket root",
+			raw:  "/buckets/warehouse/analytics/orders",
+			want: "/buckets/warehouse",
+		},
+		{
+			name: "already bucket root",
+			raw:  "/buckets/warehouse",
+			want: "/buckets/warehouse",
+		},
+		{
+			name: "relative buckets path normalized and reduced",
+			raw:  "buckets/warehouse/analytics/orders",
+			want: "/buckets/warehouse",
+		},
+		{
+			name: "non buckets path preserved",
+			raw:  "/tmp/custom/path",
+			want: "/tmp/custom/path",
+		},
+		{
+			name: "empty path",
+			raw:  "",
+			want: "",
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			if got := normalizeTableLocationMappingPath(tc.raw); got != tc.want {
+				t.Fatalf("normalizeTableLocationMappingPath(%q)=%q, want %q", tc.raw, got, tc.want)
+			}
+		})
+	}
+}