init: add contract definitions and database schema with migrations skeleton

contract/api/common.schema.json

@@ -0,0 +1,17 @@
+{
+  "$id": "contract/api/common.schema.json",
+  "type": "object",  "required": ["ok"],
+  "properties": {
+    "ok": {
+      "type": "boolean"
+    },
+    "data": {},
+    "error": {
+      "type": "object",
+      "properties": {
+        "code": { "type": "string" },
+        "message": { "type": "string" }
+      }
+    }
+  }
+}

contract/api/timeseries.schema.json

@@ -0,0 +1,18 @@
+{
+  "type": "object",
+  "required": ["points"],
+  "properties": {
+    "points": {
+      "type": "array",
+      "items": {
+        "type": "object",
+        "required": ["ts", "value"],
+        "properties": {
+          "ts": { "type": "integer" },
+          "value": {}
+        },
+        "additionalProperties": false
+      }
+    }
+  }
+}