v0.1.5 — Token savings visible in UI

What's new

Token savings stats now appear as a native system notice in the Claude Code UI
(systemMessage) — visible to the user, not passed to the model.

Previously the stats were appended to additionalContext (invisible in UI).
Correct mechanism is the top-level systemMessage field which Claude Code
renders as a separate UI notice, distinct from the conversation.

Changes

• resolve_hook.py — stats moved from additionalContext to systemMessage
• tests/ — updated assertions to verify systemMessage field and confirm
  stats do not bleed into additionalContext