feat: session recorder — save chat turns to JSONL for later replay

[VforVitorio]

What problem does this solve?

Currently all conversation history is lost when the user exits lmcode chat. Users have no way to review what the agent did in a previous session, which makes debugging and auditing harder.

Proposed solution

Record each session to a JSONL file in ~/.local/share/lmcode/sessions/ so sessions can be replayed, searched, or resumed later.

Design:

• Each session gets a unique ID (timestamp-based, e.g. 2026-03-22T14-05-00)
• Events saved: session_start, user_message, assistant_message, tool_call, tool_result, session_end
• Storage path: ~/.local/share/lmcode/sessions/<id>.jsonl (via config/paths.py)
• Event models already exist in session/models.py (stub)
• Recorder stub in session/recorder.py (needs implementation)

Scope:

• Wire up SessionRecorder in agent/core.py — emit events at each turn
• Implement session/recorder.py — append JSONL lines
• Implement session/storage.py — list + load sessions

Roadmap: v1.0 (required before session viewer can be built)

Alternatives considered

None considered.