chore(hardening): tighten repo gates — stabilize tests, docs, and vendored gossip

[Lythaeon]

Description

Harden the current repository maintenance surface without changing the SOF feature set.
This PR fixes a parallel test hazard, makes contributor checks match the documented maintenance boundary, updates the docs toolchain, and restores the maintained sof-solana-gossip all-targets surface.

Changes

Detailed list of what changed:

• crates/sof-observer/src/runtime_env.rs: make sync and async runtime-env override test helpers share one lock and add regression coverage for cross-test interference.
• Makefile.toml, CONTRIBUTING.md: tighten contributor quality gates so docs build and vendored gossip compile checks are part of the expected workflow.
• docs/gitbook/package.json, docs/gitbook/package-lock.json: refresh the Honkit/docs dependency tree and clear the docs audit warnings that were present in the previous lockfile.
• crates/sof-solana-gossip/*: restore vendored all-targets health for the maintained library/bin surface and update stale test/bench expectations.
• docs/gitbook/crates/sof-solana-gossip.md, docs/gitbook/maintainers/docs-site.md: document the actual support boundary and enforced docs-build policy.
• Any architecture/runtime/infra implications: maintenance gates now reflect the documented support surface instead of leaving docs/gossip drift outside normal review.

For slice-related changes, include:

• Affected slices: framework/runtime test harness, contributor tooling/CI surface, vendored sof-solana-gossip, docs maintainership.
• Cross-slice communication changes (if any) and why: none at runtime; changes are about reliability of tests and project maintenance gates.
• Migration requirements (if any): none.

Motivation

Business motivation:

• Keep development moving on the current feature set with more reliable contributor feedback and fewer maintenance blind spots.

Technical motivation:

• Eliminate flaky env-sensitive tests.
• Bring docs rendering and vendored gossip compile health under the same local gate contributors are told to run.
• Remove stale docs-site dependency noise and audit warnings.

Alternative approaches considered:

• Leaving the flake in place and telling contributors to run serial tests.
• Keeping gossip/docs outside the main maintenance gate.
• Ignoring the stale docs dependency tree.

Scope and impact

• Affected slices: runtime test harness, maintainer tooling, vendored gossip, docs.
• Data/API changes: none.
• Backward compatibility: fully backward compatible.
• Performance impact: none on production runtime paths.
• Security impact: improved maintainer posture by clearing stale docs dependency warnings.

Testing

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

Commands/results:

cargo test -p sof --lib
cargo test -p sof-tx --lib
cargo check --manifest-path crates/sof-solana-gossip/Cargo.toml --all-targets --locked
cd docs/gitbook && npm ci && npm run build
cd docs/gitbook && npm audit

Results: passed while validating the hardening branch work.

Related issues and documentation

• Fixes:
• Related: audit follow-up and maintenance hardening work.
• Architecture docs: docs/architecture/README.md
• Relevant ARD/ADR:
• Operations/runbook updates: maintainer/docs policy updated in GitBook maintainer docs.

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 stacked on top of docs/ts-python-sdk-spec only because that commit was already in branch history. Review/merge order after the docs PR should continue here.