feat(doctor): first-boot pre-activate fail flag (#83)

If the installer left /var/log/nomarchy-hm-preactivate.log and no Home
Manager generation exists, doctor reports ✖ with the recovery one-liner
(home-manager switch --flake ~/.nomarchy -b bak). Clears once a
generation is present. checks.doctor covers both arms.

Verified: V2 — checks.doctor green; local smoke.

agent/BACKLOG.md

@@ -55,12 +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.
 
-### 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
-points at it. Doctor gains a first-boot line: if the log shows failure
-and the HM generation is missing, print the recovery one-liner.
-
 ### 84. Dock life polish (`VISION § C`) `[big]`
 Split before starting: (a) clamshell — lid closed with external monitor
 connected must not suspend (logind lidSwitchDocked/ExternalPower audit +
@@ -126,8 +120,8 @@ 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–#82 shipped 2026-07-11. Remaining promoted: pre-activate flag,
-  dock life, hall of fame → **NEXT #83–#85**.)_
+_(#80–#83 shipped 2026-07-11. Remaining promoted: dock life `[big]`,
+  hall of fame → **NEXT #84–#85**. Split #84 before starting.)_
 
 ### v1.0 pointer