feat: add configurable mature blur threshold setting

Add new setting 'mature_blur_level' with options PG13/R/X/XXX to control
which NSFW rating level triggers blur filtering when NSFW blur is enabled.

- Backend: update preview selection logic to respect threshold
- Frontend: update UI components to use configurable threshold
- Settings: add validation and normalization for mature_blur_level
- Tests: add coverage for new threshold behavior
- Translations: add keys for all supported languages

Fixes #867

tests/utils/test_preview_selection.py

@@ -1,30 +1,7 @@
-from py.utils.preview_selection import select_preview_media
+import pytest
 
-
-def test_select_preview_prefers_safe_media_when_blurred():
-    images = [
-        {"url": "nsfw", "type": "image", "nsfwLevel": 8},
-        {"url": "mid", "type": "image", "nsfwLevel": 4},
-        {"url": "safe", "type": "image", "nsfwLevel": 1},
-    ]
-
-    selected, level = select_preview_media(images, blur_mature_content=True)
-
-    assert selected["url"] == "safe"
-    assert level == 1
-
-
-def test_select_preview_returns_lowest_when_no_safe_media():
-    images = [
-        {"url": "x", "type": "image", "nsfwLevel": 16},
-        {"url": "r", "type": "image", "nsfwLevel": 4},
-        {"url": "xx", "type": "image", "nsfwLevel": 8},
-    ]
-
-    selected, level = select_preview_media(images, blur_mature_content=True)
-
-    assert selected["url"] == "r"
-    assert level == 4
+from py.utils.constants import NSFW_LEVELS
+from py.utils.preview_selection import resolve_mature_threshold, select_preview_media
 
 
 def test_select_preview_returns_first_when_blur_disabled():
@@ -37,3 +14,36 @@ def test_select_preview_returns_first_when_blur_disabled():
 
     assert selected["url"] == "nsfw"
     assert level == 32
+
+
+@pytest.mark.parametrize(
+    ("threshold_name", "expected_url"),
+    [
+        ("PG13", "pg"),
+        ("R", "pg13"),
+        ("X", "r"),
+        ("XXX", "x"),
+    ],
+)
+def test_select_preview_respects_configurable_threshold(threshold_name, expected_url):
+    images = [
+        {"url": "xxx", "type": "image", "nsfwLevel": NSFW_LEVELS["XXX"]},
+        {"url": "x", "type": "image", "nsfwLevel": NSFW_LEVELS["X"]},
+        {"url": "r", "type": "image", "nsfwLevel": NSFW_LEVELS["R"]},
+        {"url": "pg13", "type": "image", "nsfwLevel": NSFW_LEVELS["PG13"]},
+        {"url": "pg", "type": "image", "nsfwLevel": NSFW_LEVELS["PG"]},
+    ]
+
+    selected, level = select_preview_media(
+        images,
+        blur_mature_content=True,
+        mature_threshold=NSFW_LEVELS[threshold_name],
+    )
+
+    assert selected["url"] == expected_url
+    assert level == next(item["nsfwLevel"] for item in images if item["url"] == expected_url)
+
+
+def test_resolve_mature_threshold_falls_back_to_r_for_invalid_value():
+    assert resolve_mature_threshold({"mature_blur_level": "invalid"}) == NSFW_LEVELS["R"]
+    assert resolve_mature_threshold({}) == NSFW_LEVELS["R"]