init: add contract definitions and database schema with migrations skeleton

contract/ingest/common.schema.json

@@ -0,0 +1,37 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "$id": "contract/ingest/common.schema.json",
+  "type": "object",
+  "required": ["v", "id", "type", "ts", "deviceId", "payload"],
+  "additionalProperties": false,
+  "properties": {
+    "v": {
+      "type": "integer",
+      "const": 1
+    },
+    "id": {
+      "type": "string",
+      "minLength": 1
+    },
+    "type": {
+      "type": "string",
+      "enum": ["telemetry", "event"]
+    },
+    "ts": {
+      "type": "integer",
+      "minimum": 1600000000000,
+      "description": "Unix time in milliseconds (UTC)"
+    },
+    "deviceId": {
+      "type": "string",
+      "minLength": 1
+    },
+    "payload": {
+      "type": "object"
+    },
+    "meta": {
+      "type": "object",
+      "additionalProperties": true
+    }
+  }
+}