Resolve structured DataSet members to runtime primary leaves

[masarray]

Physical FAT validation in ARSAS exposed structured FCDA members such as MMXU1.A.phsA and MMXU1.PPV.phsAB. The static membership is valid and must remain immutable, but the previously pinned semantic resolver only handled whole-DataObject FCDs or exact final DataAttributes, leaving intermediate structured members without a scalar runtime primary.

This draft change keeps the original DataSet member identity and ordering while:

• expanding only typed descendants below the exact structured member boundary;
• never crossing into sibling phases;
• preferring an engine-semantic canonical magnitude primary while retaining secondary/quality/timestamp evidence;
• projecting the mandatory application signal from the resolver's unique PrimaryValue, rather than broad catalog operational-candidate membership;
• leaving genuinely multi-primary structured members unresolved rather than guessing.

Physical-shaped regressions cover A.phsA, PPV.phsAB, sibling isolation, and whole-structure ambiguity.

The branch intentionally started from the exact ARSAS engine pin 26c85400a4da230c4429e6302847f230385b6687, because this is a consumer-driven compatibility fix rather than an adoption of unrelated newer engine work.

Exact proven engine head

bd959bc68719c52853cede272c1f562aec9900e2

Exact-head CI

.NET CI #424 — run 33481724767 — SUCCESS

• source / provenance / wording / license verification: SUCCESS
• solution build: 0 warnings / 0 errors
• engine regression suite: 700 passed / 0 failed / 0 skipped
• new physical-shaped structured-member regressions all PASS:
  • Phase_Member_Resolves_Canonical_Magnitude_Without_Sibling_Phase
  • PhasePair_Member_Resolves_Only_That_Pair_Magnitude
  • Whole_Structured_Member_With_Multiple_Phase_Magnitudes_Remains_Ambiguous
• test diagnostics artifact ID 9790219135

ARSAS consumer integration is being proven separately on feat/fat-v2-workspace-ui; this engine PR intentionally remains draft and unmerged until the physical FAT retest closes the evidence boundary.

[masarray]

Closing as safely superseded by PR #106. Exact #103 head bd959bc68719c52853cede272c1f562aec9900e2 is an ancestor of #106 head b9ee5fc9650b72e69bc81287a1e1b047ad19b054; #106 is 8 commits ahead and 0 behind. The structured DataSet primary-binding work from #103 is fully retained in #106, which adds the semantic structured InformationReport projection on top.