chore(ci): harden arch check and import hygiene — unblock branch CI

[Lythaeon]

Description

Makes the architecture boundary check portable on runners without rg and cleans up a small set of remaining absolute-path references in the core runtime/host code. This matters because the same arch-check failure can block every open PR regardless of branch-specific logic, and the import cleanup keeps the runtime code aligned with the contribution standards the project expects.

Changes

• scripts/arch-check.sh: route forbidden-import checks through the existing search helper and fix the rg argument order so the script works with or without rg installed
• crates/sof-observer/src/framework/host.rs: import TxCommitmentStatus and TransactionDispatchMode, use thread::available_parallelism(), and remove inline absolute-path references from plugin hook subscription setup
• crates/sof-observer/src/runtime.rs: import kernel-bypass queue types/helpers and thread, then replace remaining obvious absolute-path calls in the public runtime surface
• Affected slices: app/runtime, framework
• Cross-slice communication changes: none; this is import hygiene only
• Migration requirements: none

Motivation

Business motivation:

• Unblock CI on every branch that runs cargo make arch-check on a runner image without rg.
• Reduce review churn from style-only path-noise comments in core runtime files.

Technical motivation:

• Keep the boundary checker correct regardless of tool availability.
• Prefer semantic imports over repeated crate::... and std::... references in hot-path runtime code.

Alternative approaches considered:

• Installing rg in CI instead of hardening the script. That keeps the script brittle for developers and other runners, so I rejected it.
• Leaving the import cleanup for later. That would keep the same style issue alive in the most visible runtime files.

Scope and impact

• Affected slices: framework, app/runtime
• Data/API changes: none
• Backward compatibility: unchanged
• Performance impact: neutral to marginally positive from simpler helper dispatch in arch-check; no runtime behavior change
• Security impact: none

Testing

• Unit tests
• Integration tests
• Manual verification
• Performance checks (if applicable)
• Security checks (if applicable)

Commands/results:

cargo make arch-check
cargo test -p sof --lib --no-run
cargo fmt --check --all

All commands passed locally.

Related issues and documentation

• Fixes:
• Related: open perf PR stack (#89, #91, #92) depends on this shared CI portability fix
• Architecture docs: docs/architecture/README.md
• Relevant ARD/ADR: docs/architecture/ard/0001-project-structure-and-code-goals.md, docs/architecture/ard/0003-slice-dependency-contracts.md
• Operations/runbook updates: none

Reviewer checklist

• Code follows project standards and architecture constraints
• Slice boundaries are respected (docs/architecture/ard/0003-slice-dependency-contracts.md)
• Tests added/updated and passing
• Documentation updated (README/docs/operations as needed)
• No undocumented breaking change
• Performance trade-offs documented where relevant
• Security considerations addressed where relevant

Additional notes

• This PR is intentionally small and intended to merge before the remaining perf branches are restacked onto main.