fix(subscribestar): route .art creators to .adult; clear source failure on disable

Two pre-merge fixes:

1. SubscribeStar .art age wall: the 18+ cookie doesn't clear the age gate on
   the .art domain (keeps 302'ing to /age_confirmation_warning even with the
   cookie — Elasid #54116), but the same creator is reachable on .adult where
   the cookie works. _normalize_ss_host rewrites subscribestar.art →
   subscribestar.adult at request time (stored Source.url untouched), logged so
   it's visible in walk logs. .com/.adult pass through.

2. Disabling a source now clears its failure state (last_error, error_type,
   consecutive_failures) so subs you pause (not paying for) stop lingering as
   'failing'. Only the explicit disable clears — an unrelated edit to an
   already-disabled source leaves state alone.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CDgx8bQS5YrGRK76v8HUnM

tests/test_subscribestar_native.py

@@ -22,6 +22,7 @@ from backend.app.services.subscribestar_client import (
     SubscribeStarClient,
     SubscribeStarDriftError,
     _parse_ss_datetime,
+    _split_creator_url,
 )
 from backend.app.services.subscribestar_downloader import SubscribeStarDownloader
 from backend.app.services.subscribestar_ingester import (
@@ -82,6 +83,25 @@ def test_parse_ss_datetime_variants():
     assert _parse_ss_datetime("nonsense") is None
 
 
+def test_split_creator_url_rewrites_art_to_adult():
+    # The .art age wall doesn't clear with the 18+ cookie; the same creator is
+    # reachable on .adult (Elasid, event #54116). Requests must route to .adult.
+    base, slug = _split_creator_url("https://subscribestar.art/elasid")
+    assert base == "https://subscribestar.adult"
+    assert slug == "elasid"
+    # www. prefix + trailing path still normalizes the host only.
+    base, slug = _split_creator_url("https://www.subscribestar.art/elasid/posts")
+    assert base == "https://www.subscribestar.adult"
+    assert slug == "elasid"
+
+
+def test_split_creator_url_leaves_com_and_adult_untouched():
+    assert _split_creator_url("https://subscribestar.adult/sabu")[0] == \
+        "https://subscribestar.adult"
+    assert _split_creator_url("https://www.subscribestar.com/sabu")[0] == \
+        "https://www.subscribestar.com"
+
+
 def test_date_parses_when_wrapped_in_permalink_anchor():
     # Image posts wrap the date in an <a> permalink; a plain regex missed them
     # → null dates (cheunart 2026-06-17). gallery-dl's method handles both.