fix(retention): return 404 for missing policies

[rkthtrifork]

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Comprehensive Summary of your change

Return 404 Not Found when requesting a retention policy that does not exist.

Previously, the retention DAO returned Beego's raw orm.ErrNoRows, and the retention manager converted it into an untyped error. Harbor's shared HTTP error responder therefore classified the error as unknown and returned 500 Internal Server Error.

This change:

• Wraps missing retention policies with Harbor's standard NOT_FOUND error using orm.WrapNotFoundError.
• Propagates the typed error through the retention manager.
• Documents the 404 response in the API specification.
• Adds DAO and manager assertions covering the error classification and message.

This matches the existing behavior and implementation used by other ID-based resources such as robots and quotas.

Issue being fixed

No existing issue.

Please indicate you've done the following:

• Well Written Title and Summary of the PR
• Label the PR as needed. "release-note/ignore-for-release, release-note/new-feature, release-note/update, release-note/enhancement, release-note/community, release-note/breaking-change, release-note/docs, release-note/infra, release-note/deprecation"
• Accepted the DCO. Commits without the DCO will delay acceptance.
• Made sure tests are passing and test coverage is added if needed.
• Considered the docs impact and opened a new docs issue or PR with docs changes if needed in website repository.

[Copilot]

Pull request overview

Updates retention-policy lookup failures to return Harbor’s typed 404 Not Found response.

Changes:

• Wraps missing DAO records as not-found errors.
• Propagates and tests typed errors.
• Documents the API’s 404 response.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/pkg/retention/manager.go	Propagates typed DAO errors.
src/pkg/retention/manager_test.go	Verifies not-found classification and message.
src/pkg/retention/dao/retention.go	Wraps missing policies as not-found errors.
src/pkg/retention/dao/retention_test.go	Tests DAO error behavior.
api/v2.0/swagger.yaml	Documents the GET 404 response.

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[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated no new comments.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated no new comments.