feat(p10-2): k8s-manifest-resource-v1 chunker + tier2_shared helper

Splits multi-document YAML by ^---\s*$, requires apiVersion + kind string
fields per document, emits 1 chunk per recognized k8s resource. Symbol =
<kind>/<namespace>/<name> or <kind>/<name> (cluster-scoped). Invalid YAML
returns 0 chunks (handled by p10-3 paragraph fallback). Oversize >200 lines
splits into line-windows sharing the same symbol.

tier2_shared module hosts the oversize fallback + Chunk-construction helper
mirroring code_rust_ast_v1's Chunk shape. Task E (dockerfile) and Task F
(manifest) will reuse it.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/kebab-chunk/tests/fixtures/sample_k8s.yaml

@@ -0,0 +1,34 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: api-server
+  namespace: prod
+spec:
+  replicas: 3
+  selector:
+    matchLabels:
+      app: api-server
+  template:
+    metadata:
+      labels:
+        app: api-server
+    spec:
+      containers:
+      - name: api
+        image: example/api:1.2.3
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: api-server
+  namespace: prod
+spec:
+  selector:
+    app: api-server
+  ports:
+  - port: 80
+    targetPort: 8080
+---
+# Non-k8s document — apiVersion missing
+kind: ClusterIP
+foo: bar