Add POMS references to asset variables

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: MaxGhenis

policyengine_us/variables/household/assets/bank_account_assets.py

@@ -12,3 +12,4 @@ class bank_account_assets(Variable):
     unit = USD
     definition_period = YEAR
     uprating = "gov.bls.cpi.cpi_u"
+    reference = "https://secure.ssa.gov/poms.nsf/lnx/0501140200"

policyengine_us/variables/household/assets/bond_assets.py

@@ -12,3 +12,7 @@ class bond_assets(Variable):
     unit = USD
     definition_period = YEAR
     uprating = "gov.bls.cpi.cpi_u"
+    reference = (
+        "https://secure.ssa.gov/poms.nsf/lnx/0501140240",
+        "https://secure.ssa.gov/poms.nsf/lnx/0501140250",
+    )

policyengine_us/variables/household/assets/stock_assets.py

@@ -11,3 +11,4 @@ class stock_assets(Variable):
     unit = USD
     definition_period = YEAR
     uprating = "gov.bls.cpi.cpi_u"
+    reference = "https://secure.ssa.gov/poms.nsf/lnx/0501140220"