Expand Arch target domain coverage

[MaxGhenis]

Summary

• map Arch return-count targets to count-domain variables while keeping positive-support filters
• roll complete state IRS SOI deduction/credit facts up to national targets for QBI, medical, mortgage interest, charity, SALT, and ACTC-related surfaces
• translate SSA SSI category constraints to PolicyEngine target domains (is_ssi_aged, is_blind, is_ssi_disabled)

Evidence

• ============================= test session starts ==============================
  platform darwin -- Python 3.13.9, pytest-8.4.2, pluggy-1.6.0
  rootdir: /Users/maxghenis/.codex-worktrees/microplex-us-rc-main-036fa067-20260604
  configfile: pyproject.toml
  plugins: anyio-4.13.0
  collected 101 items

tests/targets/test_arch.py ............................................. [ 44%]
........ [ 52%]
tests/targets/test_arch_facts.py ....................................... [ 91%]
......... [100%]

============================= 101 passed in 2.11s ============================== -> 101 passed

• All checks passed! -> all checks passed
• Source-backed Arch coverage with current artifact inputs improved to 153/183 cells (83.6%), from 129/183 before this adapter patch.