Restructured project

- backend moved to backend directory
- added and initialized frontend with vue
- moved infrastructure files to infra directory

backend/migrations/000003_create_family_members.up.sql

@@ -0,0 +1,26 @@
+CREATE TYPE family_role AS ENUM (
+    'owner',
+    'admin',
+    'member',
+    'child'
+);
+
+CREATE TABLE family_members
+(
+    id        BIGSERIAL PRIMARY KEY,
+    family_id BIGINT      NOT NULL REFERENCES families (id) ON DELETE CASCADE,
+    user_id   BIGINT      NOT NULL REFERENCES users (id) ON DELETE CASCADE,
+    role      family_role NOT NULL DEFAULT 'member',
+    joined_at TIMESTAMP   NOT NULL DEFAULT NOW(),
+    UNIQUE (family_id, user_id)
+);
+
+
+-- быстрый поиск всех членов семьи
+CREATE INDEX idx_family_members_family_id ON family_members (family_id);
+
+-- быстрый поиск всех семей пользователя
+CREATE INDEX idx_family_members_user_id ON family_members (user_id);
+
+-- composite для частых join’ов
+CREATE INDEX idx_family_members_user_family ON family_members (user_id, family_id);