feat(ci): add lightweight CI annotation mode for threshold breaches

[xodapi]

Problem

vimit already supports threshold-based exit codes via --fail-on, but CI usage still lacks a small, machine-friendly annotation layer for warning/danger threshold breaches.

The original issue scope was too broad and mixed together:

• git metadata injection;
• hook orchestration;
• CI presets;
• request annotation.

What to do

Keep the scope narrow: add a lightweight CI-friendly annotation/output mode on top of the existing threshold logic.

Acceptance Criteria

• There is a machine-friendly annotation mode for warning/danger threshold breaches.
• The mode works with existing --fail-on behavior.
• The mode is non-interactive and suitable for CI logs.
• The implementation does not expand into full hook orchestration or git metadata plumbing.

What not to touch

• No pre-commit framework integration.
• No request mutation/annotation.
• No AGENTS workflow changes.

Supersedes #14.

[xodapi]

🤖 Начинаю выполнение. Агент: Codex

[xodapi]

✅ PR готов: #155