Add local session history and Recent sessions GUI panel

[MLyte]

Motivation

• Implement a lightweight local session history so users can quickly consult recent optimization runs without cloud or account dependencies.
• Surface the history inside the GUI for faster iteration and context when reviewing results.
• Ensure persistence behavior is covered by automated tests and bounded to avoid unbounded file growth.

Description

• Persist session summaries to a JSONL file at ~/.optimaster/session_history.jsonl with a HISTORY_LIMIT = 200 retention policy and helper EngineService.history_path().
• Append history entries from EngineService after writing session exports via a new _append_session_history() method and provide a load_recent_history() loader.
• Add a "Recent sessions" panel to the GUI (history_box, history_panel) with a Refresh history button and an automatic refresh at startup and after each optimization via _refresh_history_panel().
• Add docs/ISSUES_BRAINSTORM_2026-04-22.md describing the task and tests/test_service_history.py unit tests covering append/load and retention behavior.

Testing

• Running pytest -q without adjusting PYTHONPATH failed during collection due to import path configuration (expected in this environment).
• Running PYTHONPATH=src pytest -q executed the test suite and returned 6 passed (all tests passed).

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Codex Task