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

Parent: PolicyEngine/populace#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, #346, #158.
• Public UK transfer artifact and manifest: policyengine-uk-data#377 and related transfer/PIP work such as #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• Capital gains method choices: policyengine-uk-data#27, #28, and whether #83 is obsolete under Populace QRF/support gates.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.

Start with the parent issue and review the listed policyengine-uk-data tickets, grouping them by panel data, transfer artifacts, firm data, FIG/non-dom, capital gains, deprivation, and the microplex beta. Record for each item whether it becomes a Populace issue, is rejected, or moves elsewhere, including the intended artifact variant; done means no archived uk-data issue is the sole durable record.