feat(memory): add database schema and storage layer (Issue #88)

Add SQLAlchemy models for the Agent Memory System:
- WorkingMemory: Key-value storage with TTL for active sessions
- Episode: Experiential memories from task executions
- Fact: Semantic knowledge triples with confidence scores
- Procedure: Learned skills and procedures with success tracking
- MemoryConsolidationLog: Tracks consolidation jobs between memory tiers

Create enums for memory system:
- ScopeType: global, project, agent_type, agent_instance, session
- EpisodeOutcome: success, failure, partial
- ConsolidationType: working_to_episodic, episodic_to_semantic, etc.
- ConsolidationStatus: pending, running, completed, failed

Add Alembic migration (0005) for all memory tables with:
- Foreign key relationships to projects, agent_instances, agent_types
- Comprehensive indexes for query patterns
- Unique constraints for key lookups and triple uniqueness
- Vector embedding column placeholders (Text fallback until pgvector enabled)

Fix timezone-naive datetime.now() in types.py TaskState (review feedback)

Includes 30 unit tests for models and enums.

Closes #88

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

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

backend/tests/unit/models/memory/test_enums.py

@@ -0,0 +1,71 @@
+# tests/unit/models/memory/test_enums.py
+"""Unit tests for memory model enums."""
+
+from app.models.memory.enums import (
+    ConsolidationStatus,
+    ConsolidationType,
+    EpisodeOutcome,
+    ScopeType,
+)
+
+
+class TestScopeType:
+    """Tests for ScopeType enum."""
+
+    def test_all_values_exist(self) -> None:
+        """Test all expected scope types exist."""
+        assert ScopeType.GLOBAL.value == "global"
+        assert ScopeType.PROJECT.value == "project"
+        assert ScopeType.AGENT_TYPE.value == "agent_type"
+        assert ScopeType.AGENT_INSTANCE.value == "agent_instance"
+        assert ScopeType.SESSION.value == "session"
+
+    def test_scope_count(self) -> None:
+        """Test we have exactly 5 scope types."""
+        assert len(ScopeType) == 5
+
+
+class TestEpisodeOutcome:
+    """Tests for EpisodeOutcome enum."""
+
+    def test_all_values_exist(self) -> None:
+        """Test all expected outcome values exist."""
+        assert EpisodeOutcome.SUCCESS.value == "success"
+        assert EpisodeOutcome.FAILURE.value == "failure"
+        assert EpisodeOutcome.PARTIAL.value == "partial"
+
+    def test_outcome_count(self) -> None:
+        """Test we have exactly 3 outcome types."""
+        assert len(EpisodeOutcome) == 3
+
+
+class TestConsolidationType:
+    """Tests for ConsolidationType enum."""
+
+    def test_all_values_exist(self) -> None:
+        """Test all expected consolidation types exist."""
+        assert ConsolidationType.WORKING_TO_EPISODIC.value == "working_to_episodic"
+        assert ConsolidationType.EPISODIC_TO_SEMANTIC.value == "episodic_to_semantic"
+        assert (
+            ConsolidationType.EPISODIC_TO_PROCEDURAL.value == "episodic_to_procedural"
+        )
+        assert ConsolidationType.PRUNING.value == "pruning"
+
+    def test_consolidation_count(self) -> None:
+        """Test we have exactly 4 consolidation types."""
+        assert len(ConsolidationType) == 4
+
+
+class TestConsolidationStatus:
+    """Tests for ConsolidationStatus enum."""
+
+    def test_all_values_exist(self) -> None:
+        """Test all expected status values exist."""
+        assert ConsolidationStatus.PENDING.value == "pending"
+        assert ConsolidationStatus.RUNNING.value == "running"
+        assert ConsolidationStatus.COMPLETED.value == "completed"
+        assert ConsolidationStatus.FAILED.value == "failed"
+
+    def test_status_count(self) -> None:
+        """Test we have exactly 4 status types."""
+        assert len(ConsolidationStatus) == 4