docs(home-assistant): correct the WAL stall attribution in ha-pg sizing (REN-141)

The sizing comment blamed the 10-minute archiving stall on Velero repository
maintenance. REN-136 disproves that over seven nights:

  - sustained archiver drain is ~14 segments/min, flat whether Kopia is
    running or not, so Kopia does not slow the drain;
  - Kopia's nearest batch drifts across 02:03-02:24Z while the burst stays
    pinned to 02:13Z, and a cause that drifts 20 minutes cannot produce an
    effect fixed to the minute.

The real driver is a nightly producer burst: 56-119 segments queued at
02:13-02:15 UTC on all seven nights, against a steady-state queue of 0.
Comment now states that, and adds REN-136's stalled-night framing (6.36 GiB
free survives one stalled night, ~18.6 GiB carries about four).

Comment text only. `spec.storage.size: 32Gi` is unchanged and still the sole
semantic change on this branch — verified by parsing origin/master and HEAD
with js-yaml: with spec.storage.size masked the two parse to identical
objects.

Raised by Argus in review of #1014 as a non-blocking finding.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Co-Authored-By: Paperclip <noreply@paperclip.ing>

kubernetes/apps/home-assistant/ha-pg-cluster.yaml

@@ -42,14 +42,24 @@ spec:
     # states rows for the purge_keep_days:7 window (~4 GB).
     #
     # 20Gi left only 6.63 GiB free, and that is the number that matters here.
-    # When WAL archiving stalled for 10 minutes while Velero ran repository
-    # maintenance (REN-129), the un-archived backlog reached 1.84 GiB — 28% of
-    # that free space. Postgres cannot recycle a WAL segment until the archiver
-    # has shipped it, so a longer stall walks the volume toward full, and a
-    # full PGDATA stops the recorder outright.
+    # WAL archiving stalled for 10 minutes and the un-archived backlog reached
+    # 1.84 GiB — 28% of that free space (REN-129).
+    #
+    # That stall was first blamed on Velero repository maintenance. It is not
+    # the cause: REN-136 measured seven nights and the archiver's sustained
+    # drain (~14 segments/min, its serial ceiling) is flat whether Kopia is
+    # running or not, and Kopia's nearest batch drifts across 02:03-02:24Z
+    # while the burst stays pinned to 02:13Z. What is real is a nightly
+    # producer burst — 56-119 segments queued at 02:13-02:15 UTC on all seven
+    # nights, against a steady-state queue of 0. Postgres cannot recycle a WAL
+    # segment until the archiver has shipped it, so a burst that arrives while
+    # archiving is stalled walks the volume toward full, and a full PGDATA
+    # stops the recorder outright.
     #
     # 32Gi takes free space to ~18.6 GiB, which puts the same 1.84 GiB backlog
-    # at 10% of headroom rather than 28%. Approved by the owner on REN-135.
+    # at 10% of headroom rather than 28%. In REN-136's terms: at 6.36 GiB free
+    # one stalled night survives and two fill the volume; ~18.6 GiB carries
+    # about four. Approved by the owner on REN-135.
     # ceph-block has allowVolumeExpansion: true, so this grows in place.
     size: 32Gi
   plugins: