Handle holding quantity generation for reverse syncs correctly when not all holdings are generated for current day (#2417)

* Handle reverse calculator starting portfolio generation correctly

* Fix current_holdings to handle different dates and hide zero quantities

- Use DISTINCT ON to get most recent holding per security instead of assuming same date
- Filter out zero quantity holdings from UI display
- Maintain cash display regardless of zero balance
- Use single efficient query with proper Rails syntax

* Continue to process holdings even if one is not resolvable

* Lint fixes

app/models/holding/portfolio_snapshot.rb

@@ -0,0 +1,32 @@
+# Captures the most recent holding quantities for each security in an account's portfolio.
+# Returns a portfolio hash compatible with the reverse calculator's format.
+class Holding::PortfolioSnapshot
+  attr_reader :account
+
+  def initialize(account)
+    @account = account
+  end
+
+  # Returns a hash of {security_id => qty} representing today's starting portfolio.
+  # Includes all securities from trades (with 0 qty if no holdings exist).
+  def to_h
+    @portfolio ||= build_portfolio
+  end
+
+  private
+    def build_portfolio
+      # Start with all securities from trades initialized to 0
+      portfolio = account.trades
+        .pluck(:security_id)
+        .uniq
+        .each_with_object({}) { |security_id, hash| hash[security_id] = 0 }
+
+      # Get the most recent holding for each security and update quantities
+      account.holdings
+        .select("DISTINCT ON (security_id) security_id, qty")
+        .order(:security_id, date: :desc)
+        .each { |holding| portfolio[holding.security_id] = holding.qty }
+
+      portfolio
+    end
+end