Ingest the full raw FRS table set and assemble the UK spine as a Frame #678

Workstream E2 of the UK-migration master epic #665; child of #145. The new build entry point: every existing UK stage transforms a loaded spine; this one creates it.

First task: raw-vintage audit (blocking)

Enumerate and sha+size-pin the FRS 2023-24 tabs, WAS round 8, LCFS, ETB, and SPI vintages in the private HF repo. The parity bar is frozen at the incumbent's enhanced_frs_2023_24.h5, so the port builds at the 2023 vintage first. Any missing vintage is a hard stop — escalate to #665 before proceeding.

Scope

• Port the incumbent's 14-table FRS read (adult, child → derived person, benunit, househol, pension, oddjob, accounts, job, benefits, maint, penprov, chldcare, extchild, mortgage) as declarative artifacts in uk/source_stages.json, each tab sha+size-verified before open (the existing put2223uk.tab pattern).
• Entity/ID construction (sernum → household_id; benunit = hh×100+n; person = hh×1000+n) including the household-ID sort invariant (policyengine-uk-data#436 — the raw household table is not sernum-ordered from 2024-25 onward; positional reads scramble the grossing weight).
• gross4 → typed design weights; demographics, region, tenure, raw council-tax columns; benefit-code mapping to *_reported columns; income mapping using WEEKS_IN_YEAR uniformly (the incumbent uses bare *52 at three call sites — fix, and record the deltas as signed differences).
• New uk_runtime/frs_spine.py + a driver mode producing a Frame with design-kind weights and provenance bound to the raw-tab fingerprints.

Acceptance

• Spine passes validate_uk_national_frame; per-column nonzero shares vs the raw-only columns of efrs_parity_reference.json within declared tolerances or signed.
• Two runs byte-identical via checkpoint digests; every artifact pinned in the manifest.
• Every build attempt lands a Logbook row (Record every UK build attempt in Logbook #666 must be merged first).

UK-specificity note (required in the PR)

FRS table semantics and the ID scheme are genuinely UK; the read/verify/assemble operations should be generic kinds. The PR lists any UK-specific code beyond the declarations and why.

Depends on: E1 (shared manifest machinery), #666.