feat: preserve session name and color across /clear

Summary

/clear resets full session state, including the session name (set via /rename) and color (set via /color). These are cosmetic preferences that should ideally persist across context clears.

Expected behavior

/clear clears conversation context but preserves session metadata: name and color.

Current behavior

/clear resets name and color, requiring the user to re-run /rename and /color after every context clear.

Workaround

Re-run /rename and /color manually after each /clear.

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