docs(ep0): hub PBS-DR capacity gauge verified correct after the volume move

The last open item from the datastore relocation. Hub operator UI
(Offsite -> PBS DR) reports felhom-offsite (ep0) at 97.9 GB capacity,
12.6 GB used, 13% full - agreeing with the on-box df (98 G / 13 G / 13%).

The gauge follows the datastore's CONFIGURED PATH, so the relocation
required no hub-side change. RUNBOOK section 10.3 warned that a stale
37.2 GB reading would mean the gauge reads the wrong filesystem and
would be a real bug worth a roadmap item - it does not, and there is
no bug.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_018ARoadHBf8rHoscfiqeVZn

documentation/architecture/07-backup-architecture.md

@@ -365,8 +365,10 @@ backups/secondary/<stack>/
 > **Re-measure rather than trust this table** once a second weekly snapshot exists — the weekly
 > incremental size is still **UNMEASURED**, and it, not the total, decides the real slope.
 >
-> ⚠️ The hub's PBS-DR gauge had **not** been re-read at the time of writing; if it still reports
-> 37.2 GB it is reading the wrong filesystem, which is a real bug worth a roadmap item.
+> ✅ **The hub's PBS-DR gauge tracked the move correctly** (verified 2026-07-27, Offsite → PBS DR):
+> `felhom-offsite (ep0)` — **capacity 97.9 GB, used 12.6 GB, 13 % full**. It follows the datastore's
+> configured path, so the relocation needed no hub-side change. The feared "gauge reads the wrong
+> filesystem" bug **does not exist**.
 
 Recorded per the operator's 2026-07-26 ruling: **the datastore will be grown later; R-82 proceeds
 meanwhile.** These are measurements, not projections-of-record — re-measure before relying on them.