feat: add Guanghu persona continuity skill kernel

Part 3/4 of the recovered Fifth Domain upgrade. Applies the persona continuity skill guard from local source commit 18dfdfd without rewriting remote history.

skills/codex/guanghu-persona-skill-guard/references/experience-receipt.schema.json

@@ -0,0 +1,44 @@
+{
+  "$schema": "https://json-schema.org/draft/2020-12/schema",
+  "$id": "guanghu.ops-experience-receipt/v1",
+  "title": "Guanghu Operations Experience Receipt",
+  "type": "object",
+  "additionalProperties": false,
+  "required": [
+    "schema",
+    "receipt_id",
+    "intent",
+    "scope",
+    "input",
+    "evidence",
+    "decision",
+    "action",
+    "observed_result",
+    "correction",
+    "invariant_id",
+    "invariant",
+    "verification",
+    "receipt_path",
+    "promotion_state",
+    "recorded_at"
+  ],
+  "properties": {
+    "schema": {"const": "guanghu.ops-experience-receipt/v1"},
+    "receipt_id": {"type": "string", "minLength": 1},
+    "intent": {"type": "string", "minLength": 1},
+    "scope": {"type": "string", "minLength": 1},
+    "input": {"type": "string", "minLength": 1},
+    "evidence": {"type": "array", "items": {"type": "string"}, "minItems": 1},
+    "decision": {"type": "string", "minLength": 1},
+    "action": {"type": "string", "minLength": 1},
+    "observed_result": {"type": "string", "minLength": 1},
+    "correction": {"type": "string", "minLength": 1},
+    "invariant_id": {"type": "string", "minLength": 1},
+    "invariant": {"type": "string", "minLength": 1},
+    "verification": {"type": "array", "items": {"type": "string"}, "minItems": 1},
+    "receipt_path": {"type": "string", "minLength": 1},
+    "promotion_state": {"enum": ["CANDIDATE_ONLY", "REVIEWED", "PROMOTED_SKILL", "ENFORCED_GUARD"]},
+    "recorded_at": {"type": "string", "format": "date-time"}
+  },
+  "description": "Stores an externally explainable causal summary, never hidden reasoning or secrets. CANDIDATE_ONLY receipts cannot become hard enforcement without review, tests, and registry promotion."
+}