Fix linked account balance currency mismatch (#566)

* Fix linked account balance currency mismatch

When linking accounts from providers (Lunchflow, SimpleFIN, Enable Banking),
the initial sync was creating balances before the correct currency was known.
This caused:
1. Opening anchor entry created with default currency (USD/EUR)
2. First sync created balances with wrong currency
3. Later syncs created balances with correct currency
4. Both currency balances existed, charts showed wrong (zero) values

Changes:
- Add `skip_initial_sync` parameter to `Account.create_and_sync`
- Skip initial sync for linked accounts (provider sync handles it)
- Add currency filter to ChartSeriesBuilder query to only fetch
  balances matching the account's current currency

* Add migration script and add tests

* Update schema.rb

---------

Signed-off-by: soky srm <sokysrm@gmail.com>
Co-authored-by: sokie <sokysrm@gmail.com>

app/controllers/lunchflow_items_controller.rb

@@ -182,13 +182,18 @@ class LunchflowItemsController < ApplicationController
       end
 
       # Create the internal Account with proper balance initialization
+      # Use lunchflow_account.currency (already parsed) and skip initial sync
+      # because the provider sync will set the correct currency from the balance API
       account = Account.create_and_sync(
-        family: Current.family,
-        name: account_data[:name],
-        balance: 0, # Initial balance will be set during sync
-        currency: account_data[:currency] || "USD",
-        accountable_type: accountable_type,
-        accountable_attributes: {}
+        {
+          family: Current.family,
+          name: account_data[:name],
+          balance: 0, # Initial balance will be set during sync
+          currency: lunchflow_account.currency || "USD",
+          accountable_type: accountable_type,
+          accountable_attributes: {}
+        },
+        skip_initial_sync: true
       )
 
       # Link account to lunchflow_account via account_providers join table
@@ -605,13 +610,17 @@ class LunchflowItemsController < ApplicationController
           selected_subtype = "credit_card" if selected_type == "CreditCard" && selected_subtype.blank?
 
           # Create account with user-selected type and subtype (raises on failure)
+          # Skip initial sync - provider sync will handle balance creation with correct currency
           account = Account.create_and_sync(
-            family: Current.family,
-            name: lunchflow_account.name,
-            balance: lunchflow_account.current_balance || 0,
-            currency: lunchflow_account.currency || "USD",
-            accountable_type: selected_type,
-            accountable_attributes: selected_subtype.present? ? { subtype: selected_subtype } : {}
+            {
+              family: Current.family,
+              name: lunchflow_account.name,
+              balance: lunchflow_account.current_balance || 0,
+              currency: lunchflow_account.currency || "USD",
+              accountable_type: selected_type,
+              accountable_attributes: selected_subtype.present? ? { subtype: selected_subtype } : {}
+            },
+            skip_initial_sync: true
           )
 
           # Link account to lunchflow_account via account_providers join table (raises on failure)