fix: persona_state SET body → canonical {pad:{pleasure,arousal,dominance}} + re-vendor Tier-3 prose (v0.19.7)

worldtree-dev landed the Tier-3 persona/memory/persona_state prose docs
(c9e59ec) — shapes that serialize as freeform Any in the OpenAPI, so the
prose markdown is their source of truth. Re-vendored docs/conversation-api-spec.md
(tolerate_drift markdown pin; worldtree-spec-rev 879cefe→c9e59ec).

Consumer alignment: --set-persona-pad / _set_persona_probe was building
{pad:[list]}, but the canonical POST /sessions/{id}/persona_state body (#317)
is {pad:{pleasure,arousal,dominance}} (named dict). Aligned the probe to the
named dict + a len!=3 guard; updated contract #2's note, the set_persona_state
docstring, and the tests. The set_persona_state wrapper was already correct
(freeform pass-through) — only the CLI probe's body construction drifted.

Suite 602 green. (Also this session: heid-code-review on the #347 slice
returned unanimous zero drift across all three panel arms.)

tests/test_sessions.py

@@ -1182,9 +1182,13 @@ class TestSetPersonaState:
             return_value=httpx.Response(204)
         )
         async with httpx.AsyncClient(base_url="https://w.example") as client:
-            result = await set_persona_state(client, "s1", {"pad": [0.4, 0.1, -0.2]})
+            result = await set_persona_state(
+                client, "s1", {"pad": {"pleasure": 0.4, "arousal": 0.1, "dominance": -0.2}}
+            )
         assert result is None
-        assert _json.loads(route.calls[0].request.content) == {"pad": [0.4, 0.1, -0.2]}
+        assert _json.loads(route.calls[0].request.content) == {
+            "pad": {"pleasure": 0.4, "arousal": 0.1, "dominance": -0.2}
+        }
 
     @respx.mock
     async def test_non_204_raises(self) -> None: