feat: initial official marketplace catalog

- integrations/virustotal: VirusTotal v3 (request-based: IP & domain reports)
- templates/: fully-commented manifest + script-command example
- README: discovery rules, manifest schema, how to publish and wire into Riposte

templates/scripts/example_command.py

@@ -0,0 +1,25 @@
+"""Example script-based command implementation.
+
+Contract (Riposte sandbox):
+- Inputs are available in the global dict `__inputs__` (already parsed JSON).
+- `json`, `os` and `sys` are pre-imported — no need to import them.
+- The script MUST print exactly ONE JSON object to stdout. That object becomes
+  the command's output (`data`). Anything else on stdout breaks parsing.
+- On failure, raise an exception (the runner reports it) or exit non-zero.
+
+The filename (without .py) MUST match the command id in manifest.yaml, e.g.
+this file `example_command.py` backs the command `id: example_command`.
+"""
+
+# Inputs declared in the command's inputs_schema:
+indicator = __inputs__.get("indicator", "")
+
+# ... call an API, compute, enrich, etc. ...
+result = {
+    "indicator": indicator,
+    "verdict": "unknown",
+    "score": 0,
+}
+
+# Emit the single JSON result object.
+print(json.dumps(result))