feat: auth service + security audit fixes + cleanup legacy services

Major changes:
- Add auth-svc: JWT auth, register/login/refresh, password reset
- Add auth UI: modals, pages (/login, /register, /forgot-password)
- Add usage tracking (usage_metrics table, daily limits)
- Add tiered rate limiting (free/pro/business)
- Add LLM usage limits per tier

Security fixes:
- All repos now require userID for Update/Delete operations
- JWT middleware in chat-svc, llm-svc, agent-svc, discover-svc
- ErrNotFound/ErrForbidden errors for proper access control

Cleanup:
- Remove legacy TypeScript services/ directory
- Remove computer-svc (to be reimplemented)
- Remove old deploy/docker configs

New files:
- backend/cmd/auth-svc/main.go
- backend/internal/auth/{types,repository}.go
- backend/internal/usage/{types,repository}.go
- backend/pkg/middleware/{llm_limits,ratelimit_tiered}.go
- backend/webui/src/components/auth/*
- backend/webui/src/app/(auth)/*

Made-with: Cursor

backend/internal/db/memory_repo.go

@@ -147,17 +147,31 @@ func (r *MemoryRepository) GetContextForUser(ctx context.Context, userID string)
 	return context, nil
 }
 
-func (r *MemoryRepository) IncrementUseCount(ctx context.Context, id string) error {
-	_, err := r.db.db.ExecContext(ctx,
-		"UPDATE user_memories SET use_count = use_count + 1, last_used = NOW() WHERE id = $1",
-		id,
+func (r *MemoryRepository) IncrementUseCount(ctx context.Context, id, userID string) error {
+	result, err := r.db.db.ExecContext(ctx,
+		"UPDATE user_memories SET use_count = use_count + 1, last_used = NOW() WHERE id = $1 AND user_id = $2",
+		id, userID,
 	)
-	return err
+	if err != nil {
+		return err
+	}
+	rows, _ := result.RowsAffected()
+	if rows == 0 {
+		return ErrNotFound
+	}
+	return nil
 }
 
-func (r *MemoryRepository) Delete(ctx context.Context, id string) error {
-	_, err := r.db.db.ExecContext(ctx, "DELETE FROM user_memories WHERE id = $1", id)
-	return err
+func (r *MemoryRepository) Delete(ctx context.Context, id, userID string) error {
+	result, err := r.db.db.ExecContext(ctx, "DELETE FROM user_memories WHERE id = $1 AND user_id = $2", id, userID)
+	if err != nil {
+		return err
+	}
+	rows, _ := result.RowsAffected()
+	if rows == 0 {
+		return ErrNotFound
+	}
+	return nil
 }
 
 func (r *MemoryRepository) DeleteByUserID(ctx context.Context, userID string) error {