Structurally model remaining PTX declarations and directives

[AntonOresten]

Audit ID: FRONT-DECL-001
Status: confirmed
Severity: medium
Category: coverage_gap

Many PTX directives, declaration shapes, arrays, initializers, and related metadata are retained losslessly as opaque text but are not structurally modeled. The transpiler now rejects these nodes safely, but structural transformations and semantic round trips remain limited.

Source ledger: audit/findings/FRONT-DECL-001.toml (audit/ was removed from main in ccf6c48 — link pinned to the last commit carrying the ledger)

Completion criteria

• Inventory remaining declaration/directive forms from the PTX ISA and external corpus.
• Add structural IR nodes with lossless parse/format behavior.
• Extend normalization, canonicalization, and structural diff without dropping fields.
• Preserve ordering and scope semantics, including module and function directives.
• Add accepted and invalid grammar cells plus external-corpus round trips.
• Extend transpilation only when the emitted Julia can preserve the declaration semantics; otherwise retain explicit fail-loud rejection.
• Update the audit record to resolved, or split it into narrower declaration-family findings.