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 In doing so, some parts of the codebase have become outdated, unnecessary, or overly-complex as a natural result of this feature prioritization.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/base_query.rb

@@ -0,0 +1,42 @@
+module IncomeStatement::BaseQuery
+  private
+    def base_query_sql(family:, interval:, transactions_scope:)
+      sql = <<~SQL
+        SELECT
+          c.id as category_id,
+          c.parent_id as parent_category_id,
+          date_trunc(:interval, ae.date) as date,
+          CASE WHEN ae.amount < 0 THEN 'income' ELSE 'expense' END as classification,
+          SUM(ae.amount * COALESCE(er.rate, 1)) as total,
+          BOOL_OR(ae.currency <> :target_currency AND er.rate IS NULL) as missing_exchange_rates
+        FROM (#{transactions_scope.to_sql}) at
+        JOIN account_entries ae ON ae.entryable_id = at.id AND ae.entryable_type = 'Account::Transaction'
+        LEFT JOIN categories c ON c.id = at.category_id
+        LEFT JOIN (
+          SELECT t.*, t.id as transfer_id, a.accountable_type
+          FROM transfers t
+          JOIN account_entries ae ON ae.entryable_id = t.inflow_transaction_id
+            AND ae.entryable_type = 'Account::Transaction'
+          JOIN accounts a ON a.id = ae.account_id
+        ) transfer_info ON (
+          transfer_info.inflow_transaction_id = at.id OR
+          transfer_info.outflow_transaction_id = at.id
+        )
+        LEFT JOIN exchange_rates er ON (
+          er.date = ae.date AND
+          er.from_currency = ae.currency AND
+          er.to_currency = :target_currency
+        )
+        WHERE (
+          transfer_info.transfer_id IS NULL OR
+          (ae.amount < 0 AND transfer_info.accountable_type = 'Loan')
+        )
+        GROUP BY 1, 2, 3, 4
+      SQL
+
+      ActiveRecord::Base.sanitize_sql_array([
+        sql,
+        { target_currency: family.currency, interval: interval }
+      ])
+    end
+end