fix(install): label and explain the swap-size prompt

BACKLOG #93 (Acer live pass): the swap field appeared as a bare
prefilled number — gum never renders the placeholder once --value is
set, and the block had no section header, so nothing said what the
value meant. Add a visible "Swap & hibernation" section, two info lines
(default = RAM keeps hibernation possible; 0 = no swap), a labeled
--header on the input, and make the info + Review lines state the
outcome in full ("N GiB swapfile (enables hibernation)" /
"none (hibernation disabled)"). Default behavior unchanged (swap = RAM).

Verified: V2 — interactive KVM UI drive of the built ISO; viewed
10-swap-prompt.png (section + explanations + labeled input) and the
Review box ("Swap: 6 GiB swapfile (enables hibernation)") in
/tmp/nomarchy-v2-swap-93/; the wipe confirmation was aborted, nothing
touched. bash -n + nix flake check --no-build green.

Side-finding recorded on #112: QEMU's /dev/fd0 was listed first by the
disk picker (live repro evidence in the same artifacts).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

agent/BACKLOG.md

@@ -30,14 +30,6 @@ These are separate queue items from one real install/session pass. Preserve
 that separation when fixing them: the installer blocker, unclear installer
 copy, and post-install desktop failures have different verification paths.
 
-### 93. Installer: swap-size field lacks a clear prompt/explanation
-
-The partition value appears prefilled without a caption explaining that it is
-swap size. Keep the resolved product default (swap exactly equal to RAM), but
-label the field, state its unit/default, and explain the no-swap value. Pass =
-the summary makes the resulting swap allocation unambiguous before disk
-changes begin.
-
 ### 94. Live ISO/install: no default browser observed
 
 Chromium is the resolved default-browser decision and is present in the
@@ -155,7 +147,10 @@ effects made clear and each existing recovery path represented once.
 ### 112. Installer disk-picker safety
 
 Exclude floppy, pseudo, tiny, and otherwise non-installable devices such as
-`/dev/fd0`; never select them by default. Pass = the real install disk is clear,
+`/dev/fd0`; never select them by default. **Reproduced in QEMU 2026-07-13**
+(#93's V2 run): with OVMF the guest exposes `/dev/fd0` and the picker listed
+it FIRST — a blind Enter selected it (artifacts:
+`/tmp/nomarchy-v2-swap-93/20-review.png`, `Disk: /dev/fd0 (WILL BE ERASED)`). Pass = the real install disk is clear,
 invalid devices cannot reach destructive setup, a permanent guard covers the
 filter/default logic, and a pre-destructive KVM run proves the picker behavior.