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-channel@1.json

@@ -0,0 +1,73 @@
+{
+  "$id": "https://stella-ops.org/schemas/notify/notify-channel@1.json",
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "title": "Notify Channel",
+  "type": "object",
+  "required": [
+    "schemaVersion",
+    "channelId",
+    "tenantId",
+    "name",
+    "type",
+    "config",
+    "enabled",
+    "createdAt",
+    "updatedAt"
+  ],
+  "properties": {
+    "schemaVersion": {"type": "string", "const": "notify.channel@1"},
+    "channelId": {"type": "string"},
+    "tenantId": {"type": "string"},
+    "name": {"type": "string"},
+    "type": {
+      "type": "string",
+      "enum": ["slack", "teams", "email", "webhook", "custom"]
+    },
+    "displayName": {"type": "string"},
+    "description": {"type": "string"},
+    "config": {"$ref": "#/$defs/channelConfig"},
+    "enabled": {"type": "boolean"},
+    "labels": {"$ref": "#/$defs/stringMap"},
+    "metadata": {"$ref": "#/$defs/stringMap"},
+    "createdBy": {"type": "string"},
+    "createdAt": {"type": "string", "format": "date-time"},
+    "updatedBy": {"type": "string"},
+    "updatedAt": {"type": "string", "format": "date-time"}
+  },
+  "additionalProperties": false,
+  "$defs": {
+    "channelConfig": {
+      "type": "object",
+      "required": ["secretRef"],
+      "properties": {
+        "secretRef": {"type": "string"},
+        "target": {"type": "string"},
+        "endpoint": {"type": "string", "format": "uri"},
+        "properties": {"$ref": "#/$defs/stringMap"},
+        "limits": {"$ref": "#/$defs/channelLimits"}
+      },
+      "additionalProperties": false
+    },
+    "channelLimits": {
+      "type": "object",
+      "properties": {
+        "concurrency": {"type": "integer", "minimum": 1},
+        "requestsPerMinute": {"type": "integer", "minimum": 1},
+        "timeout": {
+          "type": "string",
+          "pattern": "^P(T.*)?$",
+          "description": "ISO 8601 duration"
+        },
+        "maxBatchSize": {"type": "integer", "minimum": 1}
+      },
+      "additionalProperties": false
+    },
+    "stringMap": {
+      "type": "object",
+      "patternProperties": {
+        ".*": {"type": "string"}
+      },
+      "additionalProperties": false
+    }
+  }
+}