ci: 👷 Enforce coverage and report test results on PRs - #73

Why

Passing tests previously provided no coverage report, minimum coverage check, or PR-visible result summary. Refs #72.

Changes

• Add ./gradlew -Pcoverage=true coverageCheck with JaCoCo, enforcing 90% line and 80% branch coverage. Merge test JVM data with separate CLI subprocess execution files without changing CLI output.
• Reuse the Linux CI test run for coverage/package verification, publish counts and thresholds in Actions, and retain HTML/XML reports for 14 days, including threshold failures. Missing JVM data or empty report counters fail verification.
• Create one bot comment per same-repository PR with test totals/passed/failed/errors/skipped, line/branch coverage and minimums, the CI result, commit, and workflow/artifact link. Re-runs update the bot comment; outdated commits and closed PRs are skipped. Missing reports are explicitly unavailable.
• Isolate comment write permission in a reporting job that reads a Markdown artifact without checking out or executing PR code. Fork and Dependabot PRs retain Actions summaries/artifacts without comments.
• Add subprocess instrumentation regression coverage and 16 dated-object response validation cases. Document usage and reporting behavior in the testing and English/Korean contribution guides.

Validation

• Latest hosted CI passed on 2337502, including the comment job. Published bot comment: 228 tests passed, 95.55% lines (2060/2156), 80.21% branches (1228/1531).
• Local coverageCheck verifyReleaseInputs passed; coverage-disabled command distribution tests passed (5 tests).
• Verified failures for missing test JVM data, missing CLI data, empty XML counters and coverage below the branch threshold. Threshold failure preserves its report/FAIL summary.
• Reporter fixture checks passed for multi-suite counts, failures/errors/skips, absent/malformed/empty reports, comment creation/update, leaving user comments intact, stale/closed PRs and missing/oversized artifacts.
• actionlint and whitespace checks passed. Local act was attempted but could not fetch actions/checkout due to an authentication error; hosted CI completed successfully.
• Native Windows and real Collector/Agent/Spring smoke checks were not run for this develop PR.

Compatibility and risks

Instrumentation is test-only and opt-in locally. Normal Linux CI enables it; ordinary tests and Windows checks keep coverage disabled. Historical release-asset repair skips the new coverage gate. No production CLI options, output formats, runtime dependencies or capture formats change. Codecov comparisons and required merge checks remain follow-up work.