Companion CI no longer uploads build logs as artifacts (regression from #6435)

[pfeerick]

Summary

PR #6682 (f194260070, "always upload build logs for CPN runs") added CI steps to linux_cpn.yml, macosx_cpn.yml, and win_cpn-64.yml that:

• Collected build/**/*.log, CMakeOutput.log, CMakeError.log, etc. into a logs/ directory after the build step
• Uploaded these as a separate <artifact_name>-logs artifact with if: always() and 30-day retention, so logs were available even on a failed build
• Had tools/build-companion.sh aggregate per-step error output into a build-summary.log via output_error_log()

PR #6435 ("WASM modules based simulation in Companion") replaced these three OS-specific workflows with a unified companion.yml + .github/actions/build_companion/action.yml, and dropped this log-collection/upload logic in the process.

Current state

• .github/actions/build_companion/action.yml's "Archive production artifacts" step only uploads ${{github.workspace}}/output
• On a build/packaging failure, output/ is empty (the package file is never copied there), so no log artifact is produced at all
• tools/build-companion.sh no longer writes a build-summary.log or copies CMake logs anywhere persistent
• The only diagnostic output available on failure is the truncated stdout in the Actions log itself

Impact

When a Companion build fails (e.g. during CMake configure, compile, or packaging), there's no way to retrieve the full build log without re-running CI with ad-hoc tail/diagnostic patches to build-companion.sh. This significantly slows down debugging CI-only failures.

Suggested fix

Restore the always-on log artifact upload from #6682 in the new unified action:

• In .github/actions/build_companion/action.yml, add a "Collect build logs" step (if: always()) that gathers build/**/*.log (and CMakeOutput.log/CMakeError.log) into a logs/ directory
• Add an "Archive build logs" step (if: always()) uploading logs/ as a <artifact_name>-logs artifact (e.g. 30-day retention)
• Optionally restore build-companion.sh's build-summary.log aggregation for a single consolidated log file

Found while investigating an unrelated AppImage packaging failure on Linux Companion (validation of EdgeTX/build-edgetx#42).