fix: Add missing labels to bracket/scale parameters

Added label metadata to 8 ParameterScale parameters that had no labels,
enabling automatic label generation for their bracket child parameters.

Parameters updated:
- gov.irs.credits.education.american_opportunity_credit.amount
- gov.irs.credits.eitc.phase_out.joint_bonus
- gov.irs.credits.premium_tax_credit.eligibility
- gov.irs.credits.premium_tax_credit.phase_out.ending_rate
- gov.irs.credits.premium_tax_credit.phase_out.starting_rate
- gov.states.dc.tax.income.credits.ptc.fraction_elderly
- gov.states.dc.tax.income.credits.ptc.fraction_nonelderly
- gov.states.dc.tax.income.rates

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: anth-volk

changelog_entry.yaml

@@ -0,0 +1,4 @@
+- bump: patch
+  changes:
+    fixed:
+      - Added missing label metadata to bracket/scale parameters that had no labels.

policyengine_us/parameters/gov/irs/credits/education/american_opportunity_credit/amount.yaml

@@ -13,6 +13,7 @@ brackets:
     rate:
       2009-01-01: 0
 metadata:
+  label: American Opportunity Credit marginal rate schedule
   type: marginal_rate
   rate_unit: /1
   threshold_unit: currency-USD

policyengine_us/parameters/gov/irs/credits/eitc/phase_out/joint_bonus.yaml

@@ -1,5 +1,6 @@
 description: Extra earned income credit phase-out start AGI for married filing jointly.
 metadata:
+  label: EITC joint filer bonus phase-out start
   rate_unit: currency-USD
   propagate_metadata_to_children: true
   threshold_unit: child

policyengine_us/parameters/gov/irs/credits/premium_tax_credit/eligibility.yaml

@@ -13,6 +13,7 @@ brackets:
     amount:
       2015-01-01: false
 metadata:
+  label: Premium Tax Credit eligibility thresholds
   type: single_amount
   threshold_unit: /1
   reference:

policyengine_us/parameters/gov/irs/credits/premium_tax_credit/phase_out/ending_rate.yaml

@@ -45,6 +45,7 @@ brackets:
       2021-01-01: 0.085
       2023-01-01: 0
 metadata:
+  label: Premium Tax Credit phase-out ending rate
   type: single_amount
   rate_unit: /1
   threshold_unit: currency-USD

policyengine_us/parameters/gov/irs/credits/premium_tax_credit/phase_out/starting_rate.yaml

@@ -45,6 +45,7 @@ brackets:
       2021-01-01: 0.085
       2023-01-01: 0
 metadata:
+  label: Premium Tax Credit phase-out starting rate
   type: single_amount
   rate_unit: /1
   threshold_unit: currency-USD

policyengine_us/parameters/gov/states/dc/tax/income/credits/ptc/fraction_elderly.yaml

@@ -1,5 +1,6 @@
 description: DC property tax credit offset is this AGI-specific fraction of US AGI for elderly.
 metadata:
+  label: DC property tax credit offset fraction (elderly)
   type: single_amount
   threshold_period: year
   threshold_unit: currency-USD  # federal AGI

policyengine_us/parameters/gov/states/dc/tax/income/credits/ptc/fraction_nonelderly.yaml

@@ -1,5 +1,6 @@
 description: DC property tax credit offset is this AGI-specific fraction of US AGI for non-elderly.
 metadata:
+  label: DC property tax credit offset fraction (non-elderly)
   type: single_amount
   threshold_period: year
   threshold_unit: currency-USD  # federal AGI

policyengine_us/parameters/gov/states/dc/tax/income/rates.yaml

@@ -1,5 +1,6 @@
 description: DC uses these income tax brackets and rates for all filing units.
 metadata:
+  label: DC income tax rates
   type: marginal_rate
   threshold_period: year
   threshold_unit: currency-USD  # non-negative DC taxable income