Add SECURITY.md and AGENTS.md for security-model discoverability

AGENTS.md

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+# AGENTS.md
+
+This file provides guidance to coding agents working with this repository.
+
+## Project Overview
+
+Apache Traffic Server Ingress Controller is a Kubernetes ingress controller for Apache Traffic Server (ATS). It watches `Ingress` / `Service` / `Endpoints` resources and translates them into ATS `remap.config` / `plugin.config` configuration; an admission webhook validates Ingress resources before the API server admits them.
+
+## Security model
+
+For security scans, vulnerability triage, security reviews, and any change touching the admission webhook, ingress-to-`remap.config` translation, RBAC, or how Kubernetes API objects cross the trust boundary, read [`SECURITY.md`](./SECURITY.md) first. The repo-specific surfaces (admission webhook, ingress routing) are documented there in addition to the umbrella model at [apache/trafficserver/SECURITY.md](https://github.com/apache/trafficserver/blob/master/SECURITY.md).

SECURITY.md

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+# Security Policy
+
+This is a project of the [Apache Software Foundation](https://apache.org/) and follows the ASF [vulnerability handling process](https://apache.org/security/#vulnerability-handling).
+
+We strongly encourage folks to report such problems to our private security mailing list first, before disclosing them publicly.
+
+# Reporting a Vulnerability
+
+To report a new vulnerability you have discovered please follow the ASF [vulnerability reporting process](https://apache.org/security/#reporting-a-vulnerability).
+
+# Security Model
+
+The Apache Traffic Server PMC's umbrella security model lives at [apache/trafficserver/SECURITY.md](https://github.com/apache/trafficserver/blob/master/SECURITY.md) and is the canonical reference for the trust boundaries that apply to the C++ core (administrative users trusted, binaries / scripts / configuration trusted, plugins in scope including `plugins/experimental/`).
+
+This repository (`apache/trafficserver-ingress-controller`) adds the Kubernetes ingress integration on top of that core, with two additional trust surfaces that the umbrella model does not cover directly:
+
+- **Kubernetes admission webhook.** The controller exposes a validating admission webhook to the API server. Webhook requests originate from the Kubernetes control plane and are authenticated by the API server's TLS bearer-token bootstrap; webhook bodies (the proposed `Ingress`, `Service`, `Endpoints`, and `ConfigMap` payloads) are treated as adversary-controlled input on the wire — admission decisions and parsing of those payloads must not crash, leak, or allow injection.
+- **Ingress routing.** Resolved `Ingress` resources are translated into Traffic Server `remap.config` / `plugin.config` directives that route HTTP traffic to upstream `Service`s. Cluster users with `Ingress` create/update privileges can influence the routing table and therefore the proxy's outbound destinations; the trust boundary is the RBAC scope on those resource kinds in the namespace.
+
+Reports that fall under either of those surfaces — admission-webhook handling, or ingress-to-`remap.config` translation — should be reported via the same ASF reporting process above. The C++ core surface (proxy data plane, plugins, configuration loading) remains governed by the umbrella model linked above.