feat(api): canon log JSON Schema + validator, enforce §7 luck boundary

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

api/tests/fixtures/canon_log_valid.json

@@ -0,0 +1,29 @@
+{
+  "schema_version": 1,
+  "player": {
+    "name": "Aldric",
+    "class_id": "sellsword",
+    "luck_descriptor": "Fortune spits on you"
+  },
+  "location": { "id": "greywater_docks", "name": "the Greywater docks" },
+  "party": [
+    { "id": "brannoc_thane", "name": "Brannoc Thane", "disposition": 40 },
+    { "id": "cadwyn_vell", "name": "Cadwyn Vell", "disposition": 15 }
+  ],
+  "recent_events": [
+    "Arrived at Greywater by barge before dawn",
+    "Brannoc recognised the harbourmaster and went quiet"
+  ],
+  "established_facts": [
+    "the eastern bridge out of Greywater is washed out",
+    "the harbourmaster is named Oda Fenn"
+  ],
+  "active_quests": [
+    { "id": "find_the_ledger", "name": "The Missing Ledger",
+      "status": "active", "objective": "Find who took Fenn's ledger" }
+  ],
+  "humiliations": [
+    { "id": "h_0001", "text": "vomited on a shrine step in front of a priest",
+      "weight": 7, "turn": 3 }
+  ]
+}