feat(lifecycle): plain-language generation diffs (#82)

nomarchy-what-changed wraps nvd into "N added, M removed, K updated"
summaries. nomarchy-rebuild / nomarchy-home print full nvd and toast
the one-liner; System › What changed? offers toast + floating report.
checks.what-changed fixtures nvd via NOMARCHY_NVD.

Verified: V2 — flake check --no-build; checks.what-changed green;
local smoke on real HM generations.

agent/BACKLOG.md

@@ -55,13 +55,6 @@ runtime-computed `resume_offset` into the boot cmdline, and the dev box runs
 exactly this layout (`/proc/cmdline` verified) but isn't Nomarchy. Steps in
 HARDWARE-QUEUE. Close #76 on PASS.
 
-### 82. Generation readability (`VISION § B`)
-"What changed last rebuild" in plain language: post-switch `nvd` /
-`nix store diff-closures` summary (n packages up/down/added) surfaced
-as a toast and/or a "What changed?" row beside System › Rollback.
-Rollback lists generations but the story is incomplete. VM assert on
-the diff text.
-
 ### 83. Doctor first-boot section: pre-activate fail flag (`VISION § A`)
 The installer leaves `/var/log/nomarchy-hm-preactivate.log` on the
 target when the theme bake fails, but nothing on the installed system
@@ -133,9 +126,8 @@ high-ROI, etc.) live in the journal + ROADMAP — not here.*
   2026-07-10). Keep #59 commented install guidance; no
   `nomarchy.hardware.nvidia.*` until a hybrid maintainer + queue.
 
-_(#80 battery health + #81 first-boot welcome shipped 2026-07-11.
-  Remaining promoted: generation readability, pre-activate flag, dock
-  life, hall of fame → **NEXT #82–#85**.)_
+_(#80–#82 shipped 2026-07-11. Remaining promoted: pre-activate flag,
+  dock life, hall of fame → **NEXT #83–#85**.)_
 
 ### v1.0 pointer