chore(release): prepare v0.5.0

[rng1995]

Summary

Prepare SkillEvaluator v0.5.0 after merging the Harbor 0.24.0 upgrade in #83, following the v0.4.0 release PR (#177).

Bump package metadata, the source version fallback, citation metadata, the developer guide example, and the root lockfile entry to 0.5.0. Cut the dated 0.5.0 - 2026-10-06 changelog section and leave a fresh Unreleased section. Dependency versions and historical release notes are unchanged.

Release Impact

This release includes the changes merged since v0.4.0: Harbor 0.24.0 (#83), configurable judge evidence budgets (#160), structured judge output and transient-error retries (#145), trajectory reconstruction from agent logs (#119), canonical native-task case identity (#161), and non-string YAML-key validation (#178).

The release notes cover Harbor's upgrade requirements, including numeric native-task rewards, wandb using cwsandbox, disabled project dotenv loading, and separate-verifier precedence. This PR prepares the release metadata; the v0.5.0 tag and GitHub Release can be published against its merge commit after validation.

Verification

• Reviewed the Contributing Guidelines; commit includes DCO sign-off.
• Updated version documentation and CHANGELOG.md; no credentials, private datasets, or proprietary benchmark content added.
• uv lock --check and uv sync --all-extras --locked --python 3.13.
• make lint and ruff check ..
• Fern 5.66.1 check: 0 errors; authenticated redirect check skipped without FERN_TOKEN.
• make build: wheel and source distribution built successfully.
• OSS boundary scan passed for source, wheel, and source distribution.
• Public benchmark fixtures passed with required source provenance.
• twine==6.2.0 check --strict passed for both distributions.
• Full local make test run on Python 3.13 with four workers: 11,250 passed, 20 skipped, and one timing-sensitive failure in test_bounded_harbor_process_timeout_preserves_redacted_diagnostic_tail (0.1-second subprocess deadline; expected diagnostic was absent). The entire affected file passed sequentially: 100 passed, 2 skipped. No test or runtime changes were made.
• Isolated installed-wheel metadata and runtime version both report 0.5.0, with Harbor 0.24.0; imports, bundled verifier, progress, and CLI smoke checks pass.

No new behavioral tests are needed for this metadata-only change; existing tests validate the release.