Replace JS-generated wide table with ERB partial and Turbo Streams

- Add _wide_table.html.erb partial (server-rendered pivot table)
- Add load_measurements helper in controller to prepare @wide_groups and
  @wide_quantities for all mutating actions
- Update index view to render the wide_table partial in #measurements-wide
- Add/update create, destroy, update turbo_stream views to refresh the
  wide table atomically after each mutation
- Remove buildWideTable() and editMeasurementWide() from application.js
- Fix create.turbo_stream.erb condition (empty readouts are vacuously all persisted)

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

app/controllers/measurements_controller.rb

@@ -6,7 +6,7 @@ class MeasurementsController < ApplicationController
   end
 
   def index
-    @measurements = current_user.readouts.includes(:quantity, :unit).order(taken_at: :desc, id: :desc)
+    load_measurements
   end
 
   def new
@@ -20,6 +20,7 @@ class MeasurementsController < ApplicationController
 
     if @readouts.present? && @readouts.all?(&:valid?)
       ActiveRecord::Base.transaction { @readouts.each(&:save!) }
+      load_measurements
       flash.now[:notice] = t('.success', count: @readouts.size)
     else
       errors = @readouts.flat_map { |r| r.errors.full_messages }
@@ -33,6 +34,7 @@ class MeasurementsController < ApplicationController
 
   def update
     if @readout.update(params.require(:readout).permit(:value, :unit_id, :taken_at))
+      load_measurements
       flash.now[:notice] = t('.success')
     else
       @user_units = current_user.units.ordered
@@ -42,6 +44,7 @@ class MeasurementsController < ApplicationController
 
   def destroy
     @readout.destroy!
+    load_measurements
     flash.now[:notice] = t('.success')
   end
 
@@ -50,4 +53,10 @@ class MeasurementsController < ApplicationController
   def find_readout
     @readout = current_user.readouts.find(params[:id])
   end
+
+  def load_measurements
+    @measurements = current_user.readouts.includes(:quantity, :unit).order(taken_at: :desc, id: :desc)
+    @wide_groups = @measurements.group_by(&:taken_at)
+    @wide_quantities = @measurements.map(&:quantity).uniq.sort_by(&:name)
+  end
 end