[FEAT] Undo :

- unity_undo_last (core tool): revert the most recent undoable MCP action as a whole; agentId targets a specific agent's last action; force opts into Unity's linear cascade. Companion to unity-mcp-plugin 2.36.0
- unity_undo_history is now an action log: per-agent history (newest-first, count/agentId filters) with undoable flags + current group, not just the current group name
- Clarify unity_undo as single-step global undo; add undoLast bridge wrapper (undo/last route)
- Core tier 68 -> 69; rich-mode tools/list budget 45KB -> 46.5KB for the new core tool (still ~61% under the 120KB ceiling)
- Tests: undo/last dispatch round-trip, core-tier pin + surface updated (51 pass)
- Bump package 2.33.0 -> 2.34.0