Remove plaid initialiser (#317)

* Remove plaid initialiser

The initializer can be safely removed because:
  - Config is lazily loaded via Provider::Registry
  - reload_configuration is called after settings updates
  - All calling code handles nil configs gracefully
  - Initial nil state is fine - config loads on first use

* Fix for missing config

* Actually don't pollute application.rb

* Add currency loading for balances

* Fix race condition on lazy load

* Allow loans to be imported in lunch flow also

* Fix currency processor

app/models/concerns/currency_normalizable.rb

@@ -0,0 +1,50 @@
+# Provides currency normalization and validation for provider data imports
+#
+# This concern provides a shared method to parse and normalize currency codes
+# from external providers (Plaid, SimpleFIN, LunchFlow), ensuring:
+# - Consistent uppercase formatting (e.g., "eur" -> "EUR")
+# - Validation of 3-letter ISO currency codes
+# - Proper handling of nil, empty, and invalid values
+#
+# Usage:
+#   include CurrencyNormalizable
+#   currency = parse_currency(api_data[:currency])
+module CurrencyNormalizable
+  extend ActiveSupport::Concern
+
+  private
+
+    # Parse and normalize a currency code from provider data
+    #
+    # @param currency_value [String, nil] Raw currency value from provider API
+    # @return [String, nil] Normalized uppercase 3-letter currency code, or nil if invalid
+    #
+    # @example
+    #   parse_currency("usd")     # => "USD"
+    #   parse_currency("EUR")     # => "EUR"
+    #   parse_currency("  gbp  ") # => "GBP"
+    #   parse_currency("invalid") # => nil (logs warning)
+    #   parse_currency(nil)       # => nil
+    #   parse_currency("")        # => nil
+    def parse_currency(currency_value)
+      # Handle nil, empty string, or whitespace-only strings
+      return nil if currency_value.blank?
+
+      # Normalize to uppercase 3-letter code
+      normalized = currency_value.to_s.strip.upcase
+
+      # Validate it's a reasonable currency code (3 letters)
+      if normalized.match?(/\A[A-Z]{3}\z/)
+        normalized
+      else
+        log_invalid_currency(currency_value)
+        nil
+      end
+    end
+
+    # Log warning for invalid currency codes
+    # Override this method in including classes to provide context-specific logging
+    def log_invalid_currency(currency_value)
+      Rails.logger.warn("Invalid currency code '#{currency_value}', defaulting to fallback")
+    end
+end