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/app/uipage.py

@@ -186,7 +186,32 @@ def to_options(model: dict, stored: dict | None = None) -> dict:
     """The options blob for a posted page model. A value equal to the stored
     one is written as stored, in the stored key order, so a save that changed
     nothing writes an identical blob (the browser reads 3.0 as 3)."""
-    out = U.ui_to_options(model)
+    return _settle(U.ui_to_options(model), stored)
+
+
+def to_options_partial(model: dict, stored: dict | None = None):
+    """(blob, [DeriveError]) for the checks: `uimodel.ui_to_options_partial`,
+    settled like `to_options`. Never saved (UX-15 F1)."""
+    out, errors = U.ui_to_options_partial(model)
+    return _settle(out, stored), errors
+
+
+def only_edits(mine: dict, base: dict, stored: dict) -> dict:
+    """The blob to save: `stored`, with the keys whose value in `mine` (this
+    page's model) differs from `base` (the model it opened) set to `mine`'s.
+    A key this page never edited keeps what is stored now, even when another
+    surface changed it meanwhile (UX-13 P4 test, F2)."""
+    edits = {k: v for k, v in mine.items()
+             if k not in base or not _same(v, base[k])}
+    gone = {k for k in base if k not in mine}
+    out = {k: copy.deepcopy(edits.get(k, v)) for k, v in stored.items()
+           if k not in gone}
+    out.update({k: copy.deepcopy(v) for k, v in edits.items()
+                if k not in out})
+    return out
+
+
+def _settle(out: dict, stored: dict | None) -> dict:
     stored = stored or {}
     for k, v in out.items():
         if k in stored and _same(v, stored[k]):
@@ -202,6 +227,21 @@ def derive_message(err: U.DeriveError) -> dict:
             "text": text}
 
 
+def derive_messages(errors, problems, notes, model, keys):
+    """The page's messages when part of the model could not become options:
+    each conversion's own sentence beside its field, then the checks of the
+    rest. A refusal or note about a key the failed conversion writes is left
+    out, because it judges the stored value, not what the page shows."""
+    failed = {k for err in errors for k in err.keys}
+    by_key, unanchored = problems_by_field(problems, keys)
+    kept = [t for k, texts in by_key.items() if k not in failed
+            for t in texts] + list(unanchored)
+    kept = [p for p in problems if p in kept]
+    notes = [n for n in notes if not set(n.keys or ()) & failed]
+    return ([derive_message(err) for err in errors]
+            + anchors(kept, notes, model, keys))
+
+
 # --------------------------------------------------------------------------- #
 # Where a sentence goes on the page
 # --------------------------------------------------------------------------- #