🔍 Overview

This PR continues the effort to standardize error message formatting across the codebase to adhere to the idiomatic Go Code Review Guidelines. Specifically, it ensures returned error strings are in lowercase and avoid ending punctuation.

Care was taken during this pass to only update standard text and strictly preserve all important capitalized acronyms/proper nouns (e.g., URL, Harbor, Ref) so that no pre-committed information or acronym capitalization is disrupted.

Fixes: #975

💡 Rationale

According to official Go guidelines:

"Error strings should not be capitalized (unless beginning with proper nouns or acronyms) or end with punctuation, since they are usually printed following other context."

These targeted changes resolve remaining capitalization style violations, resulting in cleaner and more idiomatic CLI error wrapping and logging.

🛠️ Changes Breakdown

1. Command-Line Layer (cmd/harbor/root/...)
   Artifacts & Labels:
   artifact/label/list.go — Standardized the missing argument error message.
   Projects:
   project/list.go — Standardized flag conflict errors.
   project/member/update.go — Lowercased "no members found" errors.
   Robot Accounts:
   robot/create.go, robot/delete.go, robot/list.go, robot/view.go — Standardized "permission denied" privilege errors across all robot commands.
   Tags & Retention:
   tag/retention/delete.go, tag/retention/list.go — Standardized flag conflict errors for retention rules.
   Users:
   user/create.go, user/delete.go, user/list.go, user/password.go — Standardized "permission denied" privilege errors.
   user/elevate.go — Lowercased the user confirmation and permission errors.
2. API Handlers (pkg/api/...)
   pkg/api/quota_handler.go — Standardized unexpected reference type errors (preserving Ref capitalization).
   pkg/api/retention_handler.go — Lowercased missing retention policy errors.
3. UI & Views (pkg/views/...)
   pkg/views/member/create/view.go — Lowercased empty username validation errors.
   pkg/views/quota/list/view.go — Standardized unexpected reference type errors.

✅ Verification

Compilation: Built successfully using go build.
Tests: Verified that the entire test suite passes (go test ./... returns ok).
Preservation: Verified that acronyms and specific identifiers within these files were carefully preserved to ensure no test assertions or semantic meaning was altered.