docs(testing): #132 — judge menu geometry by rendering; "just measure" was the trap

The guest's unfaithful rofi geometry was already documented in TESTING.md
§5. What was not, and what this closes, is that the bullet's fallback
advice — "measure text against the 40% window width instead" — is exactly
how #131 stayed wrong for weeks, and my own #131 fix made it stale on top
of that (the width is calc( 84ch min 65% ) now).

Measuring needs a width and a font, and both are per-theme: text menus
render through themes/<slug>/rofi.rasi, where boreal + neon-glass pinned a
fixed 620px while the rest used 40%, in fonts from Inter 11 to
JetBrainsMono 14. The item measured one combination no theme ships,
concluded "only truncates below 1920", and the truncation was live on a
2560 panel.

So §5 now says: judge by rendering — hardware, or `rofi -dmenu -theme <the
built rasi>` + `hyprctl layers` for the real width — and notes
checks.rofi-text-width guards the invariant that makes it fit, never how it
looks. Declined the other half (fixing the guest's fontconfig/icon cache):
the screenshots are useful as content checks, and a guest that lied
convincingly about spacing would be worse than one that obviously cannot.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

agent/BACKLOG.md

@@ -153,18 +153,6 @@ whether Nomarchy holds itself higher — darker label, or a darker accent mix
 for light palettes — and note `tools/check-theme-contrast.py` covers palette
 pairings only, never GTK widget surfaces. `[human]` for the aesthetic call.
 
-### 132. VM cannot judge rofi menu geometry
-
-The guest renders the picker with icons at roughly a quarter of `ui.iconSize`
-(44 → ~10px) and rows short enough that a 6-row root clips its last entry
-behind a scrollbar, though `lines = 8` and `dynamic = true` should fit it.
-Root is unchanged since before #105, so this is the guest's font/icon
-environment, not a regression — but it means `theme-shot.nix`/`menu-shot`
-screenshots are trustworthy for **menu content** and not for spacing, icon
-size, or truncation. Either fix the guest (fontconfig + icon cache in the
-test node) or document the gap in docs/TESTING.md §5 so the next agent does
-not chase it — right now nothing warns them.
-
 ### 133. No check pins the #107 legacy-name compat shim
 
 `lib.mkFlake`, doctor and lifecycle all still accept `theme-state.json`, and