feat: implement background task architecture for code quality scans

- Add status fields to ArchitectureScan model (status, started_at,
  completed_at, error_message, progress_message)
- Create database migration for new status fields
- Create background task function execute_code_quality_scan()
- Update API to return 202 with job IDs and support polling
- Add code quality scans to unified BackgroundTasksService
- Integrate scans into background tasks API and page
- Implement frontend polling with 3-second interval
- Add progress banner showing scan status
- Users can navigate away while scans run in background
- Document the implementation in architecture docs

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

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

models/database/architecture_scan.py

@@ -21,7 +21,7 @@ from app.core.database import Base
 
 
 class ArchitectureScan(Base):
-    """Represents a single run of the architecture validator"""
+    """Represents a single run of a code quality validator"""
 
     __tablename__ = "architecture_scans"
 
@@ -29,12 +29,26 @@ class ArchitectureScan(Base):
     timestamp = Column(
         DateTime(timezone=True), server_default=func.now(), nullable=False, index=True
     )
+    validator_type = Column(
+        String(20), nullable=False, index=True, default="architecture"
+    )  # 'architecture', 'security', 'performance'
+
+    # Background task status fields (harmonized architecture)
+    status = Column(
+        String(30), nullable=False, default="pending", index=True
+    )  # 'pending', 'running', 'completed', 'failed', 'completed_with_warnings'
+    started_at = Column(DateTime(timezone=True), nullable=True)
+    completed_at = Column(DateTime(timezone=True), nullable=True)
+    error_message = Column(Text, nullable=True)
+    progress_message = Column(String(255), nullable=True)  # Current step description
+
+    # Scan results
     total_files = Column(Integer, default=0)
     total_violations = Column(Integer, default=0)
     errors = Column(Integer, default=0)
     warnings = Column(Integer, default=0)
     duration_seconds = Column(Float, default=0.0)
-    triggered_by = Column(String(100))  # 'manual', 'scheduled', 'ci/cd'
+    triggered_by = Column(String(100))  # 'manual:username', 'scheduled', 'ci/cd'
     git_commit_hash = Column(String(40))
 
     # Relationship to violations
@@ -47,7 +61,7 @@ class ArchitectureScan(Base):
 
 
 class ArchitectureViolation(Base):
-    """Represents a single architectural violation found during a scan"""
+    """Represents a single code quality violation found during a scan"""
 
     __tablename__ = "architecture_violations"
 
@@ -55,7 +69,10 @@ class ArchitectureViolation(Base):
     scan_id = Column(
         Integer, ForeignKey("architecture_scans.id"), nullable=False, index=True
     )
-    rule_id = Column(String(20), nullable=False, index=True)  # e.g., 'API-001'
+    validator_type = Column(
+        String(20), nullable=False, index=True, default="architecture"
+    )  # 'architecture', 'security', 'performance'
+    rule_id = Column(String(20), nullable=False, index=True)  # e.g., 'API-001', 'SEC-001', 'PERF-001'
     rule_name = Column(String(200), nullable=False)
     severity = Column(
         String(10), nullable=False, index=True
@@ -96,17 +113,20 @@ class ArchitectureViolation(Base):
 
 
 class ArchitectureRule(Base):
-    """Architecture rules configuration (from YAML with database overrides)"""
+    """Code quality rules configuration (from YAML with database overrides)"""
 
     __tablename__ = "architecture_rules"
 
     id = Column(Integer, primary_key=True, index=True)
     rule_id = Column(
         String(20), unique=True, nullable=False, index=True
-    )  # e.g., 'API-001'
+    )  # e.g., 'API-001', 'SEC-001', 'PERF-001'
+    validator_type = Column(
+        String(20), nullable=False, index=True, default="architecture"
+    )  # 'architecture', 'security', 'performance'
     category = Column(
         String(50), nullable=False
-    )  # 'api_endpoint', 'service_layer', etc.
+    )  # 'api_endpoint', 'service_layer', 'authentication', 'database', etc.
     name = Column(String(200), nullable=False)
     description = Column(Text)
     severity = Column(String(10), nullable=False)  # Can override default from YAML