fix(cli): keep policy and provider diagnostics readable

[shiju-nv]

Summary

Policy history tables can panic when truncation splits a UTF-8 character, and provider detail hides YAML serialization failures as though the profile were absent. Use character-safe truncation and a bounded recovery diagnostic while preserving valid YAML navigation and redacted object output.

Related Issue

No issue required: corrections to diagnostic rendering and error handling.

Changes

• Reuse the existing Unicode-safe truncation helper for policy revision errors, preserving empty cells and normal ASCII output.
• Distinguish absent, valid and unserializable provider-profile YAML. Explain serialization failure and how to recover; expose the profile YAML action only after successful serialization.
• Preserve strict serialization and discard error text that may echo authored values. Cover the actual table renderer, provider display/navigation and long multibyte failures.

Testing

• mise run pre-commit passes
• Unit tests added/updated
• E2E tests added/updated (if applicable)

Checklist

• Follows Conventional Commits
• Commits are signed off (DCO)
• Architecture docs updated (if applicable)