Add physical iOS Orchard prover benchmark

[ValarDragon]

Summary

• add a release-only Rust Orchard benchmark with separate key initialization
  and complete two-Action proving timers
• add a minimal hosted XCTest app for physical iOS ARM64 devices
• emit raw samples, summary statistics, source/toolchain/device metadata, and
  thermal state as JSON
• support default, orbits-unprepared, and prepared-table prover modes
• add local-iPhone, Firebase Test Lab, BrowserStack, packaging, extraction,
  and historical-root scripts

Benchmark definition

Keygen times ProvingKey::build plus ProvingKey::verifying_key. Proof timing is
only Bundle::create_proof for one Orchard bundle containing exactly two
Actions. Bundle/RNG construction, preparation, FFI, signatures, verification,
and JSON are outside the proof timer. Prepared mode calls prepare_proving once
outside both timers.

The prepared-table comparison uses orbits-prover versus prepared-prover so
both cells have the same orbits MSM implementation and differ only by table
preparation.

Validation

• cargo fmt --all -- --check
• Cargo release checks for orbits-prover and prepared-prover
• shell syntax and plist validation
• aarch64-apple-ios release static library and signed XCTest build
• seven successful physical iPhone 17 Pro / A19 Pro / iOS 26.6 runs,
  including the six-cell source/preparation matrix
• all physical runs reported nominal thermal state at start and end

No cryptographic production behavior is changed by this PR.