feat(validation): improve user-facing schema validation errors

[saquibsaifee]

Description

• Provide a stable, safe presentation of validation failures so callers (UIs/tools) can display actionable messages instead of raw backend error objects.
• Make nested JSON schema failures more useful by preferring the most relevant jsonschema context error when available.
• Normalize XML validation log entries into the same message/path shape used for JSON.

Fixes issue: #827

AI Tool Disclosure

• My contribution does not include any AI-generated content
• My contribution includes AI-generated content, as disclosed below:
  • AI Tools: GTP Codex
  • LLMs and versions: GPT-5.3-Codex
  • Prompts: [Summarize the key prompts or instructions given to the AI tools]

Affirmation

• My code follows the CONTRIBUTING.md guidelines

[read-the-docs-community]

Documentation build overview

📚 CycloneDX Python Library | 🛠️ Build #31603563 | 📁 Comparing 8a6efce against latest (bf596c0)

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genindex.html	📝 modified
autoapi/cyclonedx/validation/index.html	📝 modified
autoapi/cyclonedx/validation/json/index.html	📝 modified