prover-bins-v5 (settle harnesses rebuilt against pinned guest)

Settle harness binaries rebuilt against the pinned confidential guest.

The v4 exec-* binaries embedded a superseded guest, so every settle proof they produced was
rejected on-chain. This release rebuilds all 19 against the pinned guest ELF.

Verification chain:

• pinned guest ELF sha256 170504091f44dcaff09ee844e78e446244078fef687eeacf6e61378961e5bba0
• derives program_vkey 0x00711089f0dc47b5512aae81461535cfd754ecbaec86dc88dc821c3ef1f4c0a4
• that vkey is present in the live pool's deployed runtime bytecode
• all 19 binaries byte-verified to embed exactly that ELF, and each asserts EXPECT_VKEY at runtime

bitcoin_prove is byte-identical to v4 (03c5ee9e…, unchanged).

A build.rs guard now hashes the guest ELF at compile time, so a drifted checkout fails the build
instead of producing binaries that prove happily and are rejected on-chain.