Add offline meal journal and secure sync

backend/migrations/005_meal_journal.sql

@@ -0,0 +1,27 @@
+-- User-owned meal journal. Photos are deliberately not stored in these rows.
+-- Apply after migrations 001-004 with a verified database backup.
+
+CREATE TABLE meal_entries (
+    id BIGINT UNSIGNED AUTO_INCREMENT PRIMARY KEY,
+    user_id INT NOT NULL,
+    client_meal_uuid CHAR(36) NOT NULL,
+    name VARCHAR(180) NOT NULL,
+    meal_type ENUM('breakfast', 'lunch', 'dinner', 'snack') NOT NULL,
+    calories DECIMAL(8,2) NOT NULL,
+    protein_grams DECIMAL(7,2) NOT NULL DEFAULT 0,
+    carbohydrate_grams DECIMAL(7,2) NOT NULL DEFAULT 0,
+    fat_grams DECIMAL(7,2) NOT NULL DEFAULT 0,
+    consumed_at DATETIME NOT NULL,
+    source ENUM('manual', 'photo_ai') NOT NULL DEFAULT 'manual',
+    notes VARCHAR(1000) NOT NULL DEFAULT '',
+    revision INT UNSIGNED NOT NULL DEFAULT 1,
+    created_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP,
+    updated_at DATETIME NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
+    UNIQUE KEY uq_meal_user_client_uuid (user_id, client_meal_uuid),
+    INDEX idx_meals_user_consumed (user_id, consumed_at DESC),
+    CONSTRAINT fk_meals_user FOREIGN KEY (user_id) REFERENCES users(id) ON DELETE CASCADE,
+    CHECK (calories >= 0 AND calories <= 10000),
+    CHECK (protein_grams >= 0 AND protein_grams <= 1000),
+    CHECK (carbohydrate_grams >= 0 AND carbohydrate_grams <= 1000),
+    CHECK (fat_grams >= 0 AND fat_grams <= 1000)
+) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;