Add target DB diagnostics dashboard

[MaxGhenis]

Summary

• add a static diagnostics dashboard for PE-native per-target loss comparisons using Cosilico design tokens
• enrich target diagnostic JSON with PolicyEngine target DB match metadata and legacy-only gap flags
• include the EITC AGI/child-count domain in the Microplex PE-native broad target profile

Tests

• uv run --extra dev --with-editable ../microplex ruff check src/microplex_us/pipelines/pe_native_scores.py src/microplex_us/policyengine/target_profiles.py tests/pipelines/test_pe_native_scores.py scripts/sync_cosilico_theme.py
• uv run --extra dev --with-editable ../microplex pytest -q tests/pipelines/test_pe_native_scores.py
• node --check dashboard/app.js
• python3 scripts/sync_cosilico_theme.py --check
• Playwright desktop/mobile smoke against http://127.0.0.1:8765/dashboard/