chore: feature flag prompt-injection-hardening (OFF)

Flag para la feature multi-issue 0019 (prompt injection hardening).
Desactivado hasta que todas las sub-issues estén completas.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

dev/feature_flags.json

@@ -1,3 +1,10 @@
 {
-  "flags": {}
+  "flags": {
+    "prompt-injection-hardening": {
+      "enabled": false,
+      "issue": "0019",
+      "description": "Hardening contra prompt injection: deny-by-default en tools, SSRF protection, path traversal, allowlists",
+      "added": "2026-03-07"
+    }
+  }
 }