Add smart combined album asset redistribution + fix locale string

Core library:
- New combine_album_assets() in asset_utils.py: smart redistribution
  of unused quota when albums return fewer assets than their share.
  Two-pass algorithm: even split then redistribute remainder.
- 6 new tests (56 total passing).

Frontend:
- Fix "leave empty to keep current" not localized in server edit.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/core/tests/test_asset_utils.py

@@ -2,6 +2,7 @@
 
 from immich_watcher_core.asset_utils import (
     build_asset_detail,
+    combine_album_assets,
     filter_assets,
     get_any_url,
     get_public_url,
@@ -183,3 +184,54 @@ class TestBuildAssetDetail:
         assert "url" not in detail
         assert "download_url" not in detail
         assert "thumbnail_url" in detail  # always present
+
+
+class TestCombineAlbumAssets:
+    def test_even_distribution(self):
+        """Both albums have plenty, split evenly."""
+        a = [_make_asset(f"a{i}") for i in range(10)]
+        b = [_make_asset(f"b{i}") for i in range(10)]
+        result = combine_album_assets({"A": a, "B": b}, total_limit=6, order_by="name")
+        assert len(result) == 6
+
+    def test_smart_redistribution(self):
+        """Album A has 1 photo, Album B has 20. Limit=10 should get 10 total."""
+        a = [_make_asset("a1", created_at="2023-03-19T10:00:00Z")]
+        b = [_make_asset(f"b{i}", created_at=f"2023-03-19T{10+i}:00:00Z") for i in range(20)]
+        result = combine_album_assets({"A": a, "B": b}, total_limit=10, order_by="name")
+        assert len(result) == 10
+        # a1 should be in result
+        ids = {r.id for r in result}
+        assert "a1" in ids
+
+    def test_redistribution_with_3_albums(self):
+        """3 albums: A has 1, B has 2, C has 20. Limit=12."""
+        a = [_make_asset("a1")]
+        b = [_make_asset("b1"), _make_asset("b2")]
+        c = [_make_asset(f"c{i}") for i in range(20)]
+        result = combine_album_assets({"A": a, "B": b, "C": c}, total_limit=12, order_by="name")
+        assert len(result) == 12
+        # All of A and B should be included
+        ids = {r.id for r in result}
+        assert "a1" in ids
+        assert "b1" in ids
+        assert "b2" in ids
+        # C fills the remaining 9
+        c_count = sum(1 for r in result if r.id.startswith("c"))
+        assert c_count == 9
+
+    def test_all_albums_empty(self):
+        result = combine_album_assets({"A": [], "B": []}, total_limit=10)
+        assert result == []
+
+    def test_single_album(self):
+        a = [_make_asset(f"a{i}") for i in range(5)]
+        result = combine_album_assets({"A": a}, total_limit=3, order_by="name")
+        assert len(result) == 3
+
+    def test_total_less_than_limit(self):
+        """Both albums together have fewer than limit."""
+        a = [_make_asset("a1")]
+        b = [_make_asset("b1"), _make_asset("b2")]
+        result = combine_album_assets({"A": a, "B": b}, total_limit=10, order_by="name")
+        assert len(result) == 3