Docs: reflect this session's findings across the repo

- top-level README.md (new): system overview, subsystem map, skills pointer,
  notable findings.
- eg4battery README/NOTES: 3 -> 6 packs (pack 6 oddball 0x01/115200); SoC drift
  + calibration section; closed-loop comms evaluated and rejected (loses per-pack
  telemetry, no native protocol, doesn't fix drift); how to force a grid charge
  via output-priority SUB.
- LVX6048 README: closed-loop pending item -> resolved decision; new "SoC
  calibration & known firmware quirks" section (POP single-digit/POP01, MCHGC
  charge-lock, re_discharge=re-discharge can't exceed float, PIRI lag, powermon
  adhoc wedge); skills pointer.
- lvx-control README: POP encoding fix, POP crc-but-applies quirk, verify-by-
  behavior, grid-charge-via-SUB usage.
- troubleshoot-inverter skill: corrected the stale "dead string per inverter"
  claim — both strings healthy; low PV is tilt/heat/shade/curtailment.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

.claude/skills/troubleshoot-inverter/SKILL.md

@@ -101,10 +101,15 @@ fallback when it didn't.
 ```bash
 "$SNAP" -w 12 -g 'lvx6048_[12]_(mppt1_input_power|mppt2_input_power|device_mode)/' 'homeassistant/sensor/+/state'
 ```
-Cross-reference array memory (`project_solar_array_config`): 9s2p per inverter, and
-there's a **suspected dead string per inverter** — one MPPT reading ~half the other,
-or roughly half nameplate in full sun, is consistent with that and worth confirming
-at the combiner, not a software bug. Zero PV at night/heavy shade is normal.
+Cross-reference array memory (`project_solar_array_config`): single MPPT per inverter,
+9s2p into it. **"Low" PV is mostly expected, not a fault** (verified 2026-06-24): at a
+clear-noon peak each inverter made ~16 A @ ~300 V — a down string would read ~10 A, so
+both parallel strings are live. The ~66%-of-nameplate output is 45° tilt (wrong for
+high summer sun), heat derate, tree shading, AND **demand-throttling** (at noon the
+battery charge pins at its cap, so the array is curtailed — not weak). To judge the
+array, measure on a clear noon with the bank *hungry* (uncurtailed): ~16 A @ 300 V then
+is healthy. Zero PV at night/heavy shade is normal. Don't diagnose "low PV" off a
+single off-peak or demand-limited sample.
 
 ## 6. Report
 State: which unit, mode, fault (decoded), cluster health, link state, what you