Decide UK panel, public transfer, and other product-scope leftovers from uk-data #148

Parent: #144.

Why

Some policyengine-uk-data tickets are not straightforward ports. They are product or architecture decisions that should not block archive as open uk-data work, but need a Populace-owned decision record.

Decisions to make

• Multi-year/panel UK data: policyengine-uk-data#345, Informed-init L0 selection: warm-start reselection for pool changes (ACS/ASEC ingest forcing function) #346, Consume Ledger target profiles for UK local metrics #158.
• Public UK transfer artifact and manifest: policyengine-uk-data#377 and related transfer/PIP work such as SNAP state take-up: fill rates use pre-mass-repair weights and the export drops the eligibility surface — calibrated caseloads don't reproduce from the artifact #419.
• Firm data: policyengine-uk-data#186.
• FIG/non-dom modelling: policyengine-uk-data#145, noting the UK moved from non-dom rules to the FIG regime from April 6, 2025.
• Capital gains method choices: policyengine-uk-data#27, EPIC: certified populace-us default correctness (gates not fully wired / reference rotted) #28, and whether Implement ACA marketplace source runtime #83 is obsolete under Populace QRF/support gates.
• IMD/deprivation: policyengine-uk-data#97.
• Microplex mp-30k-uk beta: policyengine-uk-data#422, likely obsolete if Populace UK remains the default path.

Acceptance criteria

• Each item is either promoted to a Populace implementation issue, explicitly rejected as out of scope, or assigned to another repository such as policyengine-uk.
• Decisions state the intended artifact variant, if any: compact, local, transfer, panel, or external/non-Populace.
• No archived uk-data issue remains the only durable record of the decision.