fix(install): #54 safety guards + recovery hint

Offline compose-lock failure now fail-closes (reusing the cache.nixos.org
probe) instead of falling back to a network `nix flake lock`; a disk-review
warn fires when the target already carries Windows/BitLocker/NTFS/LUKS
(before the wipe); account password requires ≥8 chars like LUKS; on HM
pre-activate failure the installer drops a NOMARCHY-DESKTOP-NOT-THEMED.txt
recovery hint in the target home so first login still shows the fix.

Worktree agent; diff reviewed + cherry-picked. V0 flake check + V1
nomarchy-install build. Password ≥8 is V0-complete; the offline/NTFS/
pre-activate scenarios are V2-pending (crafted install runs).

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

agent/BACKLOG.md

@@ -129,20 +129,15 @@ catppuccin) — btop.theme isn't contrast-checked.
   or **quarantine** (remove `waybar.css` → falls back to the generated bar),
   then capture the preview. V2 render.
 
-### 54. Installer safety + polish (promoted 2026-07-09, V0+V2)
-- **Offline fail-closed:** when the offline path is active and
-  `compose-lock.py` fails, the script currently *warns* and runs `nix flake
-  lock` (needs network) → a promised offline install can hang. Fail the
-  install with a clear message instead. (V2 offline install.)
-- **Destructive-data warning:** at disk selection/review, if `lsblk -f`/`blkid`
-  shows Windows/BitLocker/NTFS/existing-LUKS on the **chosen** disk, add one
-  explicit "data will be destroyed" line. Single whole-disk only — no
-  dual-boot path. (V0 + V2.)
-- **Password min length = 8:** the account password only requires non-empty
-  while LUKS needs ≥8 — align to one 8-char rule (not a strength meter). (V0.)
-- **HM pre-activate recovery hint:** on pre-activate failure, drop a flag
-  file / MOTD snippet on the target so first login still shows the fix
-  (observed warning this session; the install still booted themed). (V2.)
+### 54. Installer safety + polish — V2 scenarios pending
+Four guards shipped 2026-07-09 (V0/V1: bash -n, flake check, nomarchy-install
+builds): offline `compose-lock` failure now fail-closes instead of a network
+`flake lock`; disk-review `warn` when the target shows Windows/BitLocker/NTFS/
+LUKS; account password min 8 (mirrors LUKS); HM pre-activate failure drops a
+`NOMARCHY-DESKTOP-NOT-THEMED.txt` hint on the target home. **Remaining V2**
+(need crafted install scenarios): offline install actually failing closed; an
+NTFS/BitLocker disk firing the warning; the pre-activate hint landing on a
+booted target. (Password ≥8 is V0-complete.)
 
 ## LATER