feat(memory): implement memory consolidation service and tasks (#95)

- Add MemoryConsolidationService with Working→Episodic→Semantic/Procedural transfer
- Add Celery tasks for session and nightly consolidation
- Implement memory pruning with importance-based retention
- Add comprehensive test suite (32 tests)

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

backend/app/tasks/__init__.py

@@ -10,14 +10,16 @@ Modules:
     sync: Issue synchronization tasks (incremental/full sync, webhooks)
     workflow: Workflow state management tasks
     cost: Cost tracking and budget monitoring tasks
+    memory_consolidation: Memory consolidation tasks
 """
 
-from app.tasks import agent, cost, git, sync, workflow
+from app.tasks import agent, cost, git, memory_consolidation, sync, workflow
 
 __all__ = [
     "agent",
     "cost",
     "git",
+    "memory_consolidation",
     "sync",
     "workflow",
 ]