feat(doctor): battery health readout (#80)

Report-only cycle_count + retained capacity (charge_* or energy_*) as
% of design on system batteries; soft warn below 70% of design; skip
when attrs missing. NOMARCHY_POWER_SUPPLY_ROOT for the checks.doctor
fixture (test_power has no cycle/design attrs).

Verified: V2 — nix flake check --no-build; checks.doctor green (fake
BAT0 cycles/% + Device-scope ignore); local BAT0 smoke (energy_*).

agent/JOURNAL.md

@@ -19,6 +19,21 @@ Template:
 
 ---
 
+## 2026-07-11 — #80 doctor battery health readout
+- **Task:** NEXT #80 — battery health in `nomarchy-doctor` (`VISION § C`).
+- **Did:** Doctor row: `cycle_count` + retained capacity
+  (`charge_full`/`design` or `energy_*`) as `% of design`; system
+  batteries only; soft warn <70% design; skip when attrs absent.
+  `NOMARCHY_POWER_SUPPLY_ROOT` for the VM fixture. Extended
+  `checks.doctor` (fake BAT0 + Device-scope MOUSE0 ignore). HARDWARE §10,
+  ROADMAP ✓, VISION ✓; closed #80.
+- **Verified:** **V2** — `nix flake check --no-build`; `checks.doctor`
+  green; local smoke on real BAT0 (342 cycles, 81% via energy_*) + fixture.
+- **Pending:** Power-menu surface left optional/out of scope (doctor is
+  the product surface for report-only health).
+- **Next suggestion:** #81 first-boot welcome card (highest product ROI)
+  or #85 docs-only hall of fame.
+
 ## 2026-07-11 — Triage: VISION-gap PROPOSED → NEXT #80–#85 (Bernardo)
 - **Task:** Bernardo promoted five of the six fresh VISION-gap pitches
   (all but the wallpapers split, which stays LATER).