feat(docs): Add comprehensive documentation for Vexer, Vulnerability Explorer, and Zastava modules

- Introduced AGENTS.md, README.md, TASKS.md, and implementation_plan.md for Vexer, detailing mission, responsibilities, key components, and operational notes.
- Established similar documentation structure for Vulnerability Explorer and Zastava modules, including their respective workflows, integrations, and observability notes.
- Created risk scoring profiles documentation outlining the core workflow, factor model, governance, and deliverables.
- Ensured all modules adhere to the Aggregation-Only Contract and maintain determinism and provenance in outputs.

docs/modules/notify/resources/schemas/notify-event@1.json

@@ -0,0 +1,56 @@
+{
+  "$id": "https://stella-ops.org/schemas/notify/notify-event@1.json",
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "title": "Notify Event Envelope",
+  "type": "object",
+  "required": ["eventId", "kind", "tenant", "ts", "payload"],
+  "properties": {
+    "eventId": {"type": "string", "format": "uuid"},
+    "kind": {
+      "type": "string",
+      "description": "Event kind identifier (e.g. scanner.report.ready).",
+      "enum": [
+        "scanner.report.ready",
+        "scanner.scan.completed",
+        "scheduler.rescan.delta",
+        "attestor.logged",
+        "zastava.admission",
+        "feedser.export.completed",
+        "vexer.export.completed"
+      ]
+    },
+    "version": {"type": "string"},
+    "tenant": {"type": "string"},
+    "ts": {"type": "string", "format": "date-time"},
+    "actor": {"type": "string"},
+    "scope": {
+      "type": "object",
+      "properties": {
+        "namespace": {"type": "string"},
+        "repo": {"type": "string"},
+        "digest": {"type": "string"},
+        "component": {"type": "string"},
+        "image": {"type": "string"},
+        "labels": {"$ref": "#/$defs/stringMap"},
+        "attributes": {"$ref": "#/$defs/stringMap"}
+      },
+      "additionalProperties": false
+    },
+    "payload": {
+      "type": "object",
+      "description": "Event specific body; see individual schemas for shapes.",
+      "additionalProperties": true
+    },
+    "attributes": {"$ref": "#/$defs/stringMap"}
+  },
+  "additionalProperties": false,
+  "$defs": {
+    "stringMap": {
+      "type": "object",
+      "patternProperties": {
+        ".*": {"type": "string"}
+      },
+      "additionalProperties": false
+    }
+  }
+}