UX-15: setup-only mode, and the wizard fixes F1, F2, meter, step 1

A new install names no inverter. When that is the startup gate's only
refusal, the add-on now serves the setup wizard in setup-only mode instead
of exiting 78. It builds no controller, MQTT client or meter task, its
HomeAssistant is read-only (every service call refuses before sending),
Controller refuses a read-only HomeAssistant, and /action answers 409.
Any other refusal still exits 78. DECISIONS/UX-15-setup-only-mode.md.

Wizard fixes from the UX-13 P4 test:
- F1: /config/validate converts what it can, so a conversion error blocks
  its own step and the live checks still run; save 422 carries steps.
- F2: saves send the model the page opened (base); only keys this page
  changed are written onto the blob stored now.
- A meter entity missing from Home Assistant is red on the last step.
- Step 1 says the reading went down after a skip that followed a fall.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

goodwe_controller/DECISIONS/UX-13-setup-wizard.md

@@ -25,8 +25,9 @@ The page opens `#setup` only when it is opened with no route, and only when
 - **`no_power_request`**: the stored options name no inverter to control.
 - **`first_start`**: this boot found no `/data/state.json` (`Store.fresh`), the
   Store has no `setup_done` and no `auto` key, and control is not started.
-  `auto` is the key Start/Stop writes. The startup gate exits 78 before the
-  controller writes the Store, so a new install's first good boot is fresh.
+  `auto` is the key Start/Stop writes. Neither the startup gate's exit 78 nor
+  setup-only mode (UX-15) writes the Store, so a new install's first good boot
+  is fresh.
 
 "Never started" alone is not enough: both TEST-23 add-ons have `auto_start`
 off and no `auto` key, and one has run in shadow for weeks (review of PR #146,
@@ -37,14 +38,12 @@ started or stopped it, is never sent. Without a Store the answer is no. The wiza
 `setup_done` (an ISO time) to the Store. A save from the Installer view does
 not.
 
-**Not decided here, for the owner:** the add-on exits 78 before it serves the
-page when the stored options name no power request entity, which is what a
-brand-new install ships (config.yaml's `setpoint_entity: ""`). So on a truly
-new install the installer fills in "Inverter setpoint entity" on the
-Configuration tab first, and the wizard opens on the next page visit.
-Serving a setup-only page from a refused configuration would change the CFG-01
-startup gate and UX-02 §4 ("the panel is not available when it is most
-needed"), so it is left as an open question.
+**Decided since, in [[UX-15-setup-only-mode]] (owner, 2026-09-28):** a
+brand-new install ships `setpoint_entity: ""`, and it no longer exits 78. When
+naming no inverter is the gate's only refusal, the add-on serves the page in
+setup-only mode, which commands nothing, and the wizard opens with
+`no_power_request`. Setup-only mode writes no Store file, so the first-run
+rule above still holds for an install set up on the Configuration tab.
 
 ## 3. The kettle test and the sign checks
 
@@ -96,6 +95,7 @@ fingerprint was not handed out by this process, it falls back to `changed`.
   it), step blocking, the first-run rule on new and TEST-23 sites, the live
   checks, the save through the P2 path, the stale fix, and the words.
 - tools/ux13_wizard_blobs.py produces every blob the wizard can save from a new
-  install and three TEST-23 sites (88 accepted by the shipped validator). At P4
+  install and three TEST-23 sites (88 accepted by the shipped validator).
+  UX-15 added the shipped defaults as a start (setup-only mode). At P4
   all 88 were accepted by Supervisor 2026.08.0's `AppOptions`, offline, 78
   keys each.