chore(platforms): align PLATFORMS registry with PLATFORM_DEFAULT_AUTH_STRATEGY

Co-authored-by: Cursor <cursoragent@cursor.com>

tests/test_platform_alignment.py

@@ -0,0 +1,18 @@
+# -*- coding: utf-8 -*-
+"""Contract tests: PLATFORM_DEFAULT_AUTH_STRATEGY keys must resolve via PLATFORMS."""
+from db.platform_defaults import PLATFORM_DEFAULT_AUTH_STRATEGY
+from util.platforms import resolve_platform_key
+
+
+def test_platform_defaults_all_resolvable():
+    for key in PLATFORM_DEFAULT_AUTH_STRATEGY:
+        assert resolve_platform_key(key) == key
+
+
+def test_new_platform_aliases_work():
+    assert resolve_platform_key("抖音") == "douyin"
+    assert resolve_platform_key("douyin") == "douyin"
+    assert resolve_platform_key("GitHub") == "github"
+    assert resolve_platform_key("github") == "github"
+    assert resolve_platform_key("OpenAI") == "openai"
+    assert resolve_platform_key("openai") == "openai"