Release: align PTOAS with PTO ISA 0.58.1

[zhoubot]

Preserve the reviewed PTOAS 0.58 release series and correct it against the immutable PTO ISA 0.58.1 authority and canonical merged LinxISA LLVM.

Highlights:

• exact release, ABI, projection, source, catalog, and operation-contract checker
• 0.58.1 IR, verifier, EmitC, and PTO-bytecode hard break
• explicit Linx verifier and SFU pipeline mapping
• strict TPREFETCH and TIMG2COL legality
• LLVM 23 compatibility fixes without mutation-loss fallback
• canonical LLVM pin b14f16a0cccf1a360a6a64aca8606d7780db3049
• reproducible root-context Docker build with hosted Buildx builder-stage gate
• raw linxisa-v0.58.1 tag contract workflow

Local verification:

• canonical LLVM and PTOAS build passed
• check-pto 233/233
• CTest 24/24
• exact cross-root checker and negative tests passed
• PTO-BC schema and round trips passed
• independent review passed with no Critical or Important findings

Docker/Podman is unavailable on the local host, so the hosted Buildx job is the executable container-build gate.