feat(lattice): compose partial provider projections

[mgazza]

Summary

• let disjoint provider fragments contribute only the indexed auto-config slots they own
• keep aggregate target width and final array assembly in the Lattice compiler
• preserve deterministic provider/role ordering, provenance, scalar behavior, and user overrides
• reject ambiguous correlated values instead of guessing between repeated canonical slots
• keep materialization fail-closed with atomic_materializer_missing

Safety properties

• required aggregate gaps reject the whole candidate
• optional gaps become explicit None
• user overrides must match the compiler-owned aggregate width
• explicit provider role ownership disambiguates repeated canonical nodes
• unowned correlated projections fail closed when more than one aggregate slot could match
• fragment/provider order does not affect the semantic digest or projected output
• no production registration, configuration write, or materializer is added

Verification

• 64 focused and adjacent tests passed on Python 3.9, 3.11, and 3.14
• Black, Ruff, cspell, and pre-commit checks passed
• GitNexus staged change detection: LOW, two files, zero affected existing symbols or flows

Tracks Predictive-Cloud-Ltd/predbat-saas-infra#561 and #466.