fix: import the ThinkingWire that __all__ already promised

The previous commit added the name to __all__ but never bound it, so
`from polygateway import ThinkingWire` and `import *` both raised while
the whole suite stayed green — the export test names symbols one by one,
and nobody thought to add the new one.

The guard is now the invariant rather than a longer list: every name in
__all__ must be an attribute of the package.

src/polygateway/__init__.py

@@ -22,7 +22,12 @@ from polygateway.errors import (
 )
 from polygateway.ocr import OcrClient
 from polygateway.pricing import ModelPrice, PricingTable
-from polygateway.providers import DEFAULT_PROFILES, ProviderProfile, register_provider
+from polygateway.providers import (
+    DEFAULT_PROFILES,
+    ProviderProfile,
+    ThinkingWire,
+    register_provider,
+)
 from polygateway.telemetry.schema import telemetry_schema_sql
 from polygateway.thinking import (
     ThinkingCapability,