New Design System + Codebase Refresh (#1823)

Since the very first 0.1.0-alpha.1 release, we've been moving quickly to add new features to the Maybe app. In doing so, some parts of the codebase have become outdated, unnecessary, or overly-complex as a natural result of this feature prioritization.

Now that "core" Maybe is complete, we're moving into a second phase of development where we'll be working hard to improve the accuracy of existing features and build additional features on top of "core". This PR is a quick overhaul of the existing codebase aimed to:

- Establish the brand new and simplified dashboard view (pictured above)
- Establish and move towards the conventions introduced in Cursor rules and project design overview #1788
- Consolidate layouts and improve the performance of layout queries
- Organize the core models of the Maybe domain (i.e. Account::Entry, Account::Transaction, etc.) and break out specific traits of each model into dedicated concerns for better readability
- Remove stale / dead code from codebase
- Remove overly complex code paths in favor of simpler ones

app/models/income_statement/family_stats.rb

@@ -0,0 +1,47 @@
+class IncomeStatement::FamilyStats
+  include IncomeStatement::BaseQuery
+
+  def initialize(family, interval: "month")
+    @family = family
+    @interval = interval
+  end
+
+  def call
+    ActiveRecord::Base.connection.select_all(query_sql).map do |row|
+      StatRow.new(
+        classification: row["classification"],
+        median: row["median"],
+        avg: row["avg"],
+        missing_exchange_rates?: row["missing_exchange_rates"]
+      )
+    end
+  end
+
+  private
+    StatRow = Data.define(:classification, :median, :avg, :missing_exchange_rates?)
+
+    def query_sql
+      base_sql = base_query_sql(family: @family, interval: @interval, transactions_scope: @family.transactions.active)
+
+      <<~SQL
+        WITH base_totals AS (
+          #{base_sql}
+        ), aggregated_totals AS (
+          SELECT
+            date,
+            classification,
+            SUM(total) as total,
+            BOOL_OR(missing_exchange_rates) as missing_exchange_rates
+          FROM base_totals
+          GROUP BY date, classification
+        )
+        SELECT
+            classification,
+            ABS(PERCENTILE_CONT(0.5) WITHIN GROUP (ORDER BY total)) as median,
+            ABS(AVG(total)) as avg,
+            BOOL_OR(missing_exchange_rates) as missing_exchange_rates
+        FROM aggregated_totals
+        GROUP BY classification;
+      SQL
+    end
+end