fix(seaweedfs): soften master anti-affinity for small clusters (#3197)

## What this PR does

Overrides the seaweedfs master anti-affinity in the package values from
a hard `requiredDuringSchedulingIgnoredDuringExecution` hostname term to
a strong preference (`preferredDuringSchedulingIgnoredDuringExecution`,
weight 100). The selector and topologyKey are unchanged.

The vendored subchart pins the master to a hard hostname anti-affinity —
its own comment notes that emptying it is what allows single-node
deployment. With the master StatefulSet at three replicas, the surplus
master Pods stay Pending forever on clusters with fewer than three
nodes, so `helm install --wait` never returns and the S3 stack never
comes up.

Softening to a strong preference keeps the masters spread across
distinct nodes whenever the cluster has them (the scheduler only
co-locates when there is no alternative — exactly the small-cluster
case), while letting single- and dual-node clusters bring the master up.
This mirrors the posture already applied to the s3 component in the same
values file.

A helm-unittest pins the softened term (asserts the hard term is gone
and the preferred term carries the right weight, topologyKey, and
component selector) so a future subchart bump cannot silently re-harden
it.

### Screenshots

N/A — no UI changes.

### Release note

```release-note
fix(seaweedfs): soften the master anti-affinity to a preference so the S3 stack installs on clusters with fewer than three nodes
```


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **New Features**
* SeaweedFS master pods now use a softer scheduling preference for
hostname separation, improving deployment success on smaller clusters.
* **Tests**
* Added a Helm chart validation to confirm the anti-affinity behavior is
now expressed as a weighted preference (not a hard requirement),
including the expected selector and topology key.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/system/seaweedfs/tests/master_affinity_test.yaml

@@ -0,0 +1,33 @@
+suite: seaweedfs master anti-affinity
+
+# Pins the master anti-affinity override that keeps the 3-replica master
+# StatefulSet schedulable on clusters with fewer than three nodes. The upstream
+# subchart ships a HARD hostname anti-affinity
+# (requiredDuringSchedulingIgnoredDuringExecution); with three replicas that
+# leaves the surplus master Pods Pending forever on a single- or dual-node
+# cluster, so `helm install --wait` never returns. The overlay softens it to a
+# strong preference (weight 100) so the masters still spread across distinct
+# nodes when the cluster has them. This guards against a subchart bump silently
+# re-hardening the term back to required.
+
+templates:
+  - charts/seaweedfs/templates/master/master-statefulset.yaml
+
+release:
+  name: seaweedfs
+  namespace: cozy-seaweedfs
+
+tests:
+  - it: softens the master hostname anti-affinity to a preference
+    asserts:
+      - notExists:
+          path: spec.template.spec.affinity.podAntiAffinity.requiredDuringSchedulingIgnoredDuringExecution
+      - equal:
+          path: spec.template.spec.affinity.podAntiAffinity.preferredDuringSchedulingIgnoredDuringExecution[0].weight
+          value: 100
+      - equal:
+          path: spec.template.spec.affinity.podAntiAffinity.preferredDuringSchedulingIgnoredDuringExecution[0].podAffinityTerm.topologyKey
+          value: kubernetes.io/hostname
+      - equal:
+          path: spec.template.spec.affinity.podAntiAffinity.preferredDuringSchedulingIgnoredDuringExecution[0].podAffinityTerm.labelSelector.matchLabels["app.kubernetes.io/component"]
+          value: master

packages/system/seaweedfs/values.yaml

@@ -45,6 +45,28 @@ seaweedfs:
       timeoutSeconds: 30
     readinessProbe:
       timeoutSeconds: 30
+    # The upstream subchart pins the master to a HARD hostname anti-affinity
+    # (requiredDuringSchedulingIgnoredDuringExecution). With the 3-replica
+    # StatefulSet above, that makes the master unschedulable on clusters with
+    # fewer than three nodes: the surplus master Pods stay Pending forever, so
+    # `helm install --wait` never returns and Flux loops install/uninstall —
+    # the whole S3 stack never comes up. Soften it to a strong preference
+    # (weight 100) so the masters still spread across distinct nodes whenever
+    # the cluster has them, while single- and dual-node clusters can still
+    # bring the master up. Same posture already used for the s3 component
+    # below. Selector and topologyKey are unchanged from the subchart default;
+    # only required -> preferred.
+    affinity: |
+      podAntiAffinity:
+        preferredDuringSchedulingIgnoredDuringExecution:
+          - weight: 100
+            podAffinityTerm:
+              labelSelector:
+                matchLabels:
+                  app.kubernetes.io/name: {{ template "seaweedfs.name" . }}
+                  app.kubernetes.io/instance: {{ .Release.Name }}
+                  app.kubernetes.io/component: master
+              topologyKey: kubernetes.io/hostname
   volume:
     replicas: 2
     resizeHook: