feat(agent): two-stage memory system with Dream consolidation

Replace single-stage MemoryConsolidator with a two-stage architecture:

- Consolidator: lightweight token-budget triggered summarization,
  appends to HISTORY.md with cursor-based tracking
- Dream: cron-scheduled two-phase processor that analyzes HISTORY.md
  and updates SOUL.md, USER.md, MEMORY.md via AgentRunner with
  edit_file tools for surgical, fault-tolerant updates

New files: MemoryStore (pure file I/O), Dream class, DreamConfig,
/dream and /dream-log commands. 89 tests covering all components.

tests/agent/test_hook_composite.py

@@ -249,7 +249,8 @@ def _make_loop(tmp_path, hooks=None):
     with patch("nanobot.agent.loop.ContextBuilder"), \
          patch("nanobot.agent.loop.SessionManager"), \
          patch("nanobot.agent.loop.SubagentManager") as mock_sub_mgr, \
-         patch("nanobot.agent.loop.MemoryConsolidator"):
+         patch("nanobot.agent.loop.Consolidator"), \
+         patch("nanobot.agent.loop.Dream"):
         mock_sub_mgr.return_value.cancel_by_session = AsyncMock(return_value=0)
         loop = AgentLoop(
             bus=bus, provider=provider, workspace=tmp_path, hooks=hooks,