fix(tests): test_api_tags prefix tests use character: not artist: (KNOWN_KINDS dropped artist)

The two prefix-parsing tests were pinned to `artist:Eric`, but `artist`
was removed from KNOWN_KINDS in commit 4cad07a (provenance is a separate
axis from tags). The parser now keeps `artist:` literal, so the assertion
`body["name"] == "Eric"` failed.

Repointed to `character:Saber` (still in KNOWN_KINDS). Also updated the
stale `artist:` docstring example in parse_kind_prefix to `fandom:`.

Caught by [[reference-grep-pinned-tests-in-plans]] — should have grep'd
tests/ for `artist:` when shrinking KNOWN_KINDS. Banking the miss.

tests/test_api_tags.py

@@ -75,12 +75,12 @@ async def test_create_tag_name_only_defaults_to_general(client):
 
 @pytest.mark.asyncio
 async def test_create_tag_with_kind_prefix(client):
-    """IR-style: `name="artist:Eric"` without explicit kind → parsed as artist."""
-    resp = await client.post("/api/tags", json={"name": "artist:Eric"})
+    """IR-style: `name="character:Saber"` without explicit kind → parsed as character."""
+    resp = await client.post("/api/tags", json={"name": "character:Saber"})
     assert resp.status_code == 201
     body = await resp.get_json()
-    assert body["name"] == "Eric"
-    assert body["kind"] == "artist"
+    assert body["name"] == "Saber"
+    assert body["kind"] == "character"
 
 
 @pytest.mark.asyncio
@@ -88,11 +88,11 @@ async def test_explicit_kind_overrides_prefix_parsing(client):
     """If caller passes explicit kind, don't re-parse the name —
     colon and prefix stay literal."""
     resp = await client.post(
-        "/api/tags", json={"name": "artist:Eric", "kind": "general"}
+        "/api/tags", json={"name": "character:Saber", "kind": "general"}
     )
     assert resp.status_code == 201
     body = await resp.get_json()
-    assert body["name"] == "artist:Eric"
+    assert body["name"] == "character:Saber"
     assert body["kind"] == "general"