feat(epistemics): record assertions between observations and beliefs

A statement made to a mind is now three things kept apart: the observation
that it arrived, an append-only assertion (attributed actor, stance,
certainty, modality, negation, reported or quoted speech, hypothetical
status, interpretation confidence and notes), and, only for factual
assertions, one piece of evidence for a proposition belief attributed to
whoever actually stands behind it. Reported speech is attributed to the
person reported and weighed as second-hand; hypotheticals, questions and
imperatives create no belief; expressed doubt counts against; a possibly
sarcastic remark is recorded with low interpretation confidence rather
than guessed at. Interpretation is deterministic code; a model may enrich
the claim list but never sets stance or confidence.

Association no longer treats conversational turns as world events:
hypotheticals, questions, requests and consecutive turns by one speaker
cannot seed causal hypotheses.

Adds internal/epistemics, migration 0018, the assertions API, assertions
on belief pages and in belief detail, a shared end-to-end test harness
(tests/harness), end-to-end tests for eight speech patterns, and updates
the milestone test to the new provenance.

docs/openapi.json

@@ -2626,6 +2626,118 @@
     }
    }
   },
+  "/api/v1/minds/{mind}/assertions": {
+   "get": {
+    "operationId": "assertionsList",
+    "summary": "list assertions: who took what stance on which proposition",
+    "x-required-role": "observer",
+    "tags": [
+     "minds"
+    ],
+    "responses": {
+     "200": {
+      "description": "OK",
+      "content": {
+       "application/json": {
+        "schema": {
+         "type": "object"
+        }
+       }
+      }
+     },
+     "401": {
+      "$ref": "#/components/responses/Error"
+     },
+     "403": {
+      "$ref": "#/components/responses/Error"
+     },
+     "404": {
+      "$ref": "#/components/responses/Error"
+     }
+    },
+    "parameters": [
+     {
+      "name": "mind",
+      "in": "path",
+      "required": true,
+      "schema": {
+       "type": "string"
+      },
+      "description": "mind slug or id"
+     },
+     {
+      "name": "actor",
+      "in": "query",
+      "schema": {
+       "type": "string"
+      }
+     },
+     {
+      "name": "belief",
+      "in": "query",
+      "schema": {
+       "type": "string"
+      }
+     },
+     {
+      "name": "stance",
+      "in": "query",
+      "schema": {
+       "type": "string"
+      }
+     },
+     {
+      "name": "limit",
+      "in": "query",
+      "schema": {
+       "type": "integer"
+      }
+     }
+    ]
+   }
+  },
+  "/api/v1/minds/{mind}/assertions/actors": {
+   "get": {
+    "operationId": "assertionActors",
+    "summary": "summarise asserting actors",
+    "x-required-role": "observer",
+    "tags": [
+     "minds"
+    ],
+    "responses": {
+     "200": {
+      "description": "OK",
+      "content": {
+       "application/json": {
+        "schema": {
+         "type": "object"
+        }
+       }
+      }
+     },
+     "401": {
+      "$ref": "#/components/responses/Error"
+     },
+     "403": {
+      "$ref": "#/components/responses/Error"
+     },
+     "404": {
+      "$ref": "#/components/responses/Error"
+     }
+    },
+    "parameters": [
+     {
+      "name": "mind",
+      "in": "path",
+      "required": true,
+      "schema": {
+       "type": "string"
+      },
+      "description": "mind slug or id"
+     }
+    ]
+   }
+  },
   "/api/v1/minds/{mind}/beliefs": {
    "get": {
     "operationId": "beliefsList",