feat(live): #57 Install Nomarchy desktop entry + Tools row

Always-visible install surface on the live ISO: xdg.desktopEntries
(Terminal=true) plus Tools › Install Nomarchy (self-gated on
nomarchy-install on PATH). Welcome toast mentions the app. Close #57.

Verified: V1 (live eval + HM menu rebuild). V2 pending: ISO smoke.

agent/BACKLOG.md

@@ -77,15 +77,6 @@ last log lines + `nomarchy-doctor` instead of a raw Nix wall. Likely
 home: menu rebuild wrapper and/or control-center path. Cost: medium
 pkgs/menu; V1 + V2 smoke of the failure path (can force a bad eval).
 
-### 57. Live: one always-visible “Install Nomarchy” action
-Install is only in: 3s notify-send toast, getty helpLine, and tribal
-knowledge of `nomarchy-install`. **One** durable surface on the live
-host only: e.g. `xdg.desktopEntries` (Terminal=true) **or** a single
-Tools/System menu item that opens a terminal into `nomarchy-install`.
-Prefer that over more install-time questions. Also fix stale
-`hosts/live.nix` header (“No installer yet”) if still present. Cost:
-`live.nix` only; V1 ISO rebuild + V2 smoke.
-
 ### 58. `nomarchy-detect-hw` CLI (post-install re-probe)
 HARDWARE.md §8. Installer already has pure `nomarchy_detect_hw` stdout
 protocol (MODULE / NOMARCHY / DETAIL). Ship it as a package on PATH that
@@ -201,7 +192,7 @@ nomarchy-menu usage string, secondary docs, always-on pieces → #47.)_
   `btop.theme` for the three identity themes still open. Cost: asset capture;
   V3 visual.
 
-_(Generated Waybar missing identity-bar affordances → **#63**.)_
+_(Generated Waybar missing identity-bar affordances → **#63** ✓ 2026-07-10.)_
 
 - **summer-* CSS under-styles status module states**
   summer-day/night include modules in selectors but largely lack