feat: view specific history by ID or path

[insign]

Addresses #16.02 in ROADMAP.md.

Changes:

• Adds history_target support to Args.
• Implements ContextManager::show_specific_history.
• Resolves paths passed as arguments to absolute paths for comparison.
• Safely truncates messages by chars().take(200) to avoid UTF-8 boundary panics.

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PR created automatically by Jules for task 17854370819313630223 started by @insign

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