Add wide view and inline editing to Measurements page

The Measurements page gains a compact/wide view toggle (persisted in
localStorage). The wide view is a pivot table: rows = time points,
columns = quantity names (alphabetical), cells = value + delete button.

Clicking a value in either view opens an inline edit panel (Turbo Stream)
without leaving the page. The panel shows the quantity name, value input,
unit selector, taken_at picker, and Update/Cancel buttons.

Changes:
- MeasurementsController: add edit/update actions; order by taken_at desc
- measurements/index: compact table + wide container, view-toggle buttons
- measurements/_readout: data-* attributes for JS pivot builder; edit link
- measurements/_edit_panel, _edit_form, _edit_form_close,
  edit.turbo_stream, update.turbo_stream: inline edit views
- application.js: groupMeasurements, buildWideTable (alphabetical cols),
  getMeasurementsView / setMeasurementsView, editMeasurementWide,
  readoutUnitChanged, setDefaultUnit
- application.css: compact/wide visibility rules, .wide-cell flex layout,
  button.link reset, .items-table .form td alignment
- Pictograms: view-rows.svg, view-columns.svg (view-toggle icons)
- Locale: view_compact/view_wide toggle labels, edit link, update.success
- Tests: system tests for compact inline edit and wide view edit panel

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

config/locales/en.yml

@@ -97,13 +97,18 @@ en:
       taken_at_html: Measurement taken at 
     index:
       new_measurement: Add measurement
+      view_compact: Compact view
+      view_wide: Wide view
     readout:
+      edit: Edit
       destroy: Delete
     create:
       success:
         one: Recorded 1 measurement.
         other: Recorded %{count} measurements.
       no_readouts: No readouts selected.
+    update:
+      success: Measurement updated.
     destroy:
       success: Measurement deleted.
   quantities: