Settings tab

Everything that was previously a curl command now has a surface: surroundings,
site geometry, the matrix, the psychrometric flag, and the maintenance actions.

Changes persist to data/state/settings.json, not config.yaml. That file is
hand-annotated and hand-edited per station, and rewriting it from an API would
destroy the comments and risk clobbering something the owner set. The overlay is
applied last in load_config, so a dashboard change beats both the file and the
environment, and deleting the overlay reverts everything. Written atomically via
a temp file so a crash cannot truncate it.

Every field applies live. A settings page that needs a restart is one people
stop trusting, so site geometry is re-read per sample, the compensator flag is
set on the live object, and the display picks up its rate the next frame.

Two deliberate frictions. Selecting a surroundings pill only stages it: nothing
is recorded until you press the button, because that writes a discontinuity
marker and queues a retrain. And changing altitude or the psychrometric flag
says outright that the stored history is now inconsistent and offers the
re-derive, rather than leaving a silent mismatch.

Verified in a browser: pills stage and apply, the toggle round-trips, re-derive
ran 6201 rows in 0.29 s from the button, all six tabs report zero scrollbars and
zero clipping, zero console errors.

README.md

@@ -160,8 +160,8 @@ permanently.
 
 ## The dashboard
 
-Five tabs, one viewport, no scrolling on desktop. Below 1024 px the constraint is
-released, because pinning five panels into a phone viewport produces unreadable
+Six tabs, one viewport, no scrolling on desktop. Below 1024 px the constraint is
+released, because pinning six panels into a phone viewport produces unreadable
 eight-pixel type.
 
 | Tab | Answers |
@@ -170,6 +170,7 @@ eight-pixel type.
 | **History** | What did it do, over any timeframe you ask for |
 | **Models and Calibration** | Has the model earned its confidence, and the calibration inputs |
 | **Stats for Nerds** | Every internal the estimator and the 18 learners are carrying |
+| **Settings** | Surroundings, site geometry, the matrix, and maintenance actions |
 | **Methods** | How the whole thing is wired, and how each stage fails |
 
 Live carries the current readings, the observed-and-forecast chart with its 90%