feat: record the reasoning verdict in telemetry

This issue surfaced only because someone ran a slow suite that is
excluded by default and had not been run for eighteen days. As a column
it becomes a query: which model stopped being observable, and when.

The emitter unwraps the enum to a plain str at the single _record exit.
asyncpg makes no promise about encoding a str subclass, and a telemetry
write that fails is downgraded to one warning — it would not crash, it
would just quietly cost the Postgres path a column. Normalising at the
emitter follows what tenant_id, meta and sampling already do.

The column is appended last in COLUMNS and in both DDLs. An existing
table can only take ALTER at the end, so putting it anywhere else
forks the physical column order between a freshly built database and a
backfilled one.

tests/unit/test_ports.py

@@ -244,7 +244,7 @@ class TestTelemetryRecorderSignature:
         params = inspect.signature(TelemetryRecorder.record_llm_call).parameters
         assert {"tenant_id", "meta"} <= set(params)
 
-    @pytest.mark.parametrize("name", ["tenant_id", "meta"])
+    @pytest.mark.parametrize("name", ["tenant_id", "meta", "thinking_observation"])
     def test_caller_dimensions_have_no_default(self, name):
         import inspect