feat(ceph): serve reads from the local OSD (#576)

Measuring VLAN 40 for the traffic-class split turned up a share of the
management segment that is not management: the node's Ceph client
talking to OSDs on the other two nodes, sourced from the node address
on mgmt0.

Ceph sends every client read to the acting primary of the PG, which
with three OSDs is remote two times out of three. Read affinity has the
client read from the replica in its own CRUSH location instead.

The preconditions hold here. replicapool and cephfs/data0 are size 3
over failureDomain host across three nodes, so every object has a copy
on every node. The OSDs are created under zone buckets
(root=default host=k8s-N zone=<name>) and the nodes carry
topology.kubernetes.io/zone, which is in Rook's default
crushLocationLabels. Ceph is v20.2.4 and the kernel 6.18, against a
documented minimum of 5.8.

Writes are unaffected: they always go to the primary, and the
replication behind them already rides the VLAN 49 cluster network.

cephfs-ci is size 2, so a local replica is not guaranteed there and the
client falls back to the primary.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

kubernetes/infrastructure/rook-ceph-cluster/cephcluster.yaml

@@ -126,6 +126,16 @@ spec:
     addressRanges:
       cluster:
         - 10.99.0.0/29
+  # Reads go to the OSD in the client's own CRUSH location. crushLocationLabels
+  # is unset, so Rook's default list applies; of those the nodes carry
+  # topology.kubernetes.io/zone, one zone per node, matching the zone buckets
+  # the OSDs are created under.
+  #
+  # Passed as a krbd/mount option at map time, so a volume keeps its current
+  # behaviour until it is remounted.
+  csi:
+    readAffinity:
+      enabled: true
   # Nodes listed explicitly, not useAllNodes: under useAllNodes the operator
   # re-provisions an OSD on any node whose device still carries a BlueStore
   # signature, so purging an OSD before pulling its drive is impossible — it