Cashflow should use default period (and related) (#328)

* Fix cashflow and outflows widgets to respect user's default period preference

Resolves issue #118 where the Cashflow and Outflows widgets on the dashboard
were hardcoded to use a 30-day period instead of respecting the user's default
period preference setting.

Changes:
- Updated @cashflow_period to use Current.user&.default_period as fallback
- Updated @outflows_period to use Current.user&.default_period as fallback
- Both now follow the same pattern as the Periodable concern's set_period method

This ensures consistency across all dashboard widgets - Net Worth, Cashflow,
and Outflows now all respect the user's preference.

* Synchronize period selection across all dashboard widgets

All three dashboard widgets (Net Worth, Cashflow, and Outflows) now use
a single shared period parameter, ensuring consistent data magnitudes
across the dashboard.

Changes:
- Simplified controller to use single @period for all three widgets
- Removed widget-specific period parameters (cashflow_period, outflows_period)
- All widgets now use the shared 'period' parameter
- All period dropdowns use turbo_frame: "_top" to reload entire page
- Removed turbo_frame_tags from dashboard view for cleaner implementation

User experience improvement:
- Changing the period in any widget now updates all three widgets
- Ensures data consistency and easier comparison across widgets
- Maintains respect for user's default period preference

* Make Net Worth widget title styling consistent with Cashflow and Outflows

Changed Net Worth title from <p> with text-sm/text-secondary to <h2> with
text-lg to match the consistent styling used by Cashflow and Outflows widgets.

This provides a more unified visual appearance across all dashboard widgets.

---------

Co-authored-by: Claude <noreply@anthropic.com>

app/views/pages/dashboard.html.erb

@@ -29,24 +29,20 @@
 
 <div class="w-full space-y-6 pb-24">
   <% if Current.family.accounts.any? %>
-    <%= turbo_frame_tag "cashflow_sankey_section" do %>
-      <section class="bg-container py-4 rounded-xl shadow-border-xs mb-6">
-        <%= render partial: "pages/dashboard/cashflow_sankey", locals: {
-          sankey_data: @cashflow_sankey_data,
-          period: @cashflow_period
-        } %>
-      </section>
-    <% end %>
+    <section class="bg-container py-4 rounded-xl shadow-border-xs mb-6">
+      <%= render partial: "pages/dashboard/cashflow_sankey", locals: {
+        sankey_data: @cashflow_sankey_data,
+        period: @period
+      } %>
+    </section>
 
     <% if @outflows_data[:categories].present? %>
-      <%= turbo_frame_tag "outflows_donut_section" do %>
-        <section class="bg-container py-4 rounded-xl shadow-border-xs mb-6">
-          <%= render partial: "pages/dashboard/outflows_donut", locals: {
-            outflows_data: @outflows_data,
-            period: @outflows_period
-          } %>
-        </section>
-      <% end %>
+      <section class="bg-container py-4 rounded-xl shadow-border-xs mb-6">
+        <%= render partial: "pages/dashboard/outflows_donut", locals: {
+          outflows_data: @outflows_data,
+          period: @period
+        } %>
+      </section>
     <% end %>
 
     <section class="bg-container py-4 rounded-xl shadow-border-xs">