feat: ingest State Hub session tokens without booking them

Store mixed measured/estimated/superseded aggregates as session-token
evidence. Map kinds onto the evidence-basis vocabulary, keep unknown
months unknown, and refuse to post the snapshot as booked spend or
resource-control usage.

tests/fixtures/session-tokens-2026-08.json

@@ -0,0 +1,60 @@
+{
+  "schema_version": "0.1",
+  "record_type": "session_token_evidence",
+  "record_id": "session-tokens:state-hub:2026-08",
+  "revision_of": null,
+  "source_system": "state-hub",
+  "period_start": "2026-08-01",
+  "period_end": "2026-08-31",
+  "captured_at": "2026-08-15T12:00:00Z",
+  "source_evidence": [
+    "state-hub:/token-events/aggregate/?month=2026-08"
+  ],
+  "totals": {
+    "measured": {
+      "tokens_in": 100,
+      "tokens_out": 50,
+      "event_count": 2,
+      "confidence": "1.0"
+    },
+    "allocated": {
+      "tokens_in": 20,
+      "tokens_out": 10,
+      "event_count": 1,
+      "confidence": "0.70",
+      "method": "state-hub-task-share"
+    },
+    "estimated": {
+      "tokens_in": 1000,
+      "tokens_out": 500,
+      "event_count": 3,
+      "confidence": "0.35"
+    },
+    "superseded": {
+      "tokens_in": 800,
+      "tokens_out": 200,
+      "event_count": 1,
+      "confidence": "0.0"
+    }
+  },
+  "associations": [
+    {
+      "scope": "repo",
+      "scope_id": "cce28433-34ce-4ab1-9ab4-4dac9222c802",
+      "label": "fin-hub",
+      "measurement_kind": "measured",
+      "tokens_in": 100,
+      "tokens_out": 50,
+      "event_count": 2
+    },
+    {
+      "scope": "workplan",
+      "scope_id": "88de5e03-a53f-4b62-a0a7-1365756da2d7",
+      "label": "FIN-WP-0007",
+      "measurement_kind": "estimated",
+      "tokens_in": 1000,
+      "tokens_out": 500,
+      "event_count": 3
+    }
+  ]
+}