feat(P02): l1-s3 manifest + mock_apply (T-2.7)

---ci---
phase: 2
milestone: v1.0
status: execute
persona: infra-stub-engineer
task: T-2.7
requirements:
  covered: [REQ-02, REQ-03]
---/ci---

Wave 1, task T-2.7. Creates modules/l1/l1-s3/ with manifest.yaml
(flat inputs per D-017) and the uniform mock_apply.sh (D-007 + D-018).

modules/l1/l1-s3/manifest.yaml

@@ -0,0 +1,13 @@
+name: l1-s3
+kind: l1
+description: Object store primitive
+inputs:
+  bucket_name:
+    description: Globally unique name of the S3 bucket
+    type: string
+  region:
+    description: AWS region the bucket lives in
+    type: string
+  retention_days:
+    description: Number of days to retain objects before expiration
+    type: string

modules/l1/l1-s3/mock_apply.sh

@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+set -euo pipefail
+echo "[L1: l1-s3] applying..."
+sleep 1
+echo "[L1: l1-s3] OK"
+exit 0