orchestrator: carry device count in table type

[Daniiiil1]

Summary

• carry the device count as a const generic on DeviceTable
• accept a fixed-size device array instead of an erased slice
• require Chain<N> to be constructed from DeviceTable<_, _, N>
• remove the remaining runtime capacity assertion from table-to-chain conversion

Why

This is the fixed-size-array part of OpenPRoT#404, rebased onto the single-source design in #26 as requested in review. The table's validated length now travels in the type, so a chain with a mismatched capacity is rejected by the compiler instead of at runtime.

Validation

• npx --yes @bazel/bazelisk test //services/orchestrator/config:all //services/orchestrator/sm:orchestrator_sm_test //target/mock:all
• rustup run stable rustfmt --edition 2024 --check on all changed Rust files
• git diff --check