fix(patreon): handle the /cw/ creator-URL prefix in vanity extraction

A source URL like https://www.patreon.com/cw/Atole resolved vanity='cw' — the
vanity regex only skipped a /c/ prefix, so Patreon's current /cw/ ("creator
workspace") form fell through to the bare-vanity branch and captured the prefix
instead of the slug. Every /cw/ source then failed campaign-id resolution
(API + page-scrape both looked up "cw"). Operator-confirmed 2026-06-07 via the
new error text: source_url='.../cw/Atole'; vanity='cw'.

Add cw/ to the optional prefix group (ordered before c/ so the longer prefix
wins), and have the creator-page fallback try the /cw/ form too. Test covers
bare / c/ / cw/ extraction and that id: URLs stay non-vanity.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

tests/test_patreon_resolver.py

@@ -169,3 +169,17 @@ async def test_for_source_unresolvable_returns_none():
     cid, resolved = await resolve_campaign_id_for_source("not-a-patreon-url", None, {})
     assert cid is None
     assert resolved is None
+
+
+def test_extract_vanity_handles_all_path_prefixes():
+    """Patreon serves the vanity bare and under c/ and cw/ prefixes; all must
+    yield the creator slug, not the prefix (operator-flagged 2026-06-07: a
+    /cw/Atole source resolved vanity='cw')."""
+    from backend.app.services.patreon_resolver import extract_vanity
+
+    assert extract_vanity("https://www.patreon.com/Atole") == "Atole"
+    assert extract_vanity("https://www.patreon.com/c/Atole") == "Atole"
+    assert extract_vanity("https://www.patreon.com/cw/Atole") == "Atole"
+    assert extract_vanity("https://patreon.com/cw/Atole") == "Atole"
+    # id: URLs are NOT vanities (handled by the id path).
+    assert extract_vanity("https://www.patreon.com/id:123") is None