fix(codegen): preserve borrowed projected slice views

[sanohiro]

Summary

• accept exact array-to-slice view retypes while checking borrowed projection paths against their owning aggregate type
• preserve scalar and AoS record-array element types through borrowed Option projections
• reject forged sibling-field/type mismatches before LLVM lowering
• cover Some/None, whole-program/per-unit builds, repeated borrows, and owner reuse

Request 21

This closes the Align compiler side of align-llm Request 21. Consumer pin adoption and verification remain align-llm-owned follow-up work.

Verification

• focused align_codegen_llvm malformed-retype owner
• focused align_driver whole-program/per-unit runtime owner
• align-llm work-in-progress corpus built with the fixed local compiler
• code-tier scripts/pre-pr.sh (owner checks, bounded gate, lint ratchet, Clippy)
• one full-diff inspection plus a clean changed-slice inspection for the test-only ratchet correction