UX-54: a Forecast tab with the sun, the house and each battery's level, per hour

A new tab beside Home and Batteries for today and tomorrow: the solar
forecast, the solar measured so far, the house's expected use and each
battery's expected level, with the plan's own charge and give blocks under it.

- Blocks are Home's: today's are the plan's `runs`, tomorrow's come from the
  same builders (`homeview.runs_for()`), in the plan lines' words.
- The sun is what solarfc reads; a daily total is spread over the bell and the
  tab says so. The house is HouseProfile.estimator(), as the plan reads it.
- The level is new: `daycurve.curve()` gives each battery the role
  `modetrade.decide()` gives it and moves it hour by hour inside the plan's
  floor and ceiling. It is an estimate and counts on `solar_trust_pct`.
- Built on request (`GET forecast`), no Home Assistant call. Measured solar is
  kept per hour in memory from the reading control already takes.
- A part not known yet is a note: modes off, no forecast, learning, no
  forecast for tomorrow, a monthly cycle, no level, stopped, shadow.

No decision, command, timing or option key changes. Found, not changed:
`dayplan.plan()` over-counts a state-only forecast (DECISIONS/UX-54).

Co-Authored-By: Claude <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Bdqr7PiaHcBnzPituu2yTC

goodwe_controller/DOCS.md

@@ -3530,6 +3530,21 @@ the peak limit, the batteries' switches and modes, and shadow mode, each
 marked "Applies right away" or "Applies after a restart". **Installer** shows
 every setting.
 
+### The Forecast screen
+
+The **Forecast** tab shows today and tomorrow, hour by hour: the solar forecast,
+the solar measured so far today, the house's expected use, and each battery's
+expected level. Under each battery's chart are its planned blocks, in the same
+words as Home. A block is there only where the add-on plans one.
+
+The level is an estimate. It counts on `solar_trust_pct` of the forecast, as the
+plan does, and stays between the battery's low and high levels. A forecast that
+gives one total for the day (Forecast.Solar) is spread over the hours, and the
+screen says so. Where a part is not known yet (battery modes off, no forecast,
+still learning your house, no forecast for tomorrow) the screen says that
+instead of drawing an empty chart. It changes nothing in control, and it asks
+Home Assistant for nothing: it is built when you open it.
+
 ### Setup, for a new install
 
 The **Setup** tab walks an installer through six steps: the meter, the