feat: add mistral vibe agent integration

[sfroment]

Add vibe (mistral-vibe) agent to herdr, following the grok session-identity pattern adapted for vibe's post_agent hook system.

• detect: Agent::Vibe variant, label/executable/lookup, vibe.toml manifest
• agent_resume: source, reserved-source, plan, session_ref_from_snapshot
• integration: IntegrationTarget::Vibe, env, types, config_edit, targets, actions, registry, hook asset
• cli: parse_integration_target + usage
• config: sound, model, config-reference

Co-authored-by: pipeline

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[kangal-bot]

Hi @sfroment, thanks for your interest in contributing!

Herdr automatically admits focused bug fixes from contributors who are not maintainers when the title uses fix: ... or fix(scope): ... and the patch changes no more than 20 files and 1,000 total added or deleted lines.

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Patch size: 19 changed files, 434 changed lines.

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