feat(P02): l1-eks-fargate manifest + mock_apply (T-2.1)

---ci---
phase: 2
milestone: v1.0
status: execute
persona: infra-stub-engineer
task: T-2.1
requirements:
  covered: [REQ-02, REQ-03]
---/ci---

Wave 1, task T-2.1. Creates modules/l1/l1-eks-fargate/ with manifest.yaml
(flat inputs per D-017) and the uniform mock_apply.sh (D-007 + D-018).
Also removes the now-obsolete modules/l1/.gitkeep.

modules/l1/l1-eks-fargate/manifest.yaml

@@ -0,0 +1,13 @@
+name: l1-eks-fargate
+kind: l1
+description: Serverless container compute substrate
+inputs:
+  cluster_name:
+    description: Name of the EKS cluster to target
+    type: string
+  region:
+    description: AWS region the cluster runs in
+    type: string
+  cpu_arch:
+    description: CPU architecture for Fargate pods (x86_64 or arm64)
+    type: string

modules/l1/l1-eks-fargate/mock_apply.sh

@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+set -euo pipefail
+echo "[L1: l1-eks-fargate] applying..."
+sleep 1
+echo "[L1: l1-eks-fargate] OK"
+exit 0