[PBI] Notification data model and database schema

[cjlapao]

Description

Define and implement the core Notification struct and its per-user database schema using GORM. This is the foundational data layer all other PBIs depend on — nothing else can be built until the model and schema are in place and reviewed.

User Story

As a backend engineer, I want a well-defined, GORM-annotated notification model persisted to the database, so that all other components in the notification system have a stable, tested data contract to build against.

Acceptance Criteria

• Model defined: A Notification struct is created with all required fields: id (UUID), user_id, type (enum: alert, warning, info, success), title, message, host_id (nullable), record_id (nullable), correlation_id (nullable), actions (serialised JSON), meta (serialised as []map[string]string), is_read (bool, default false), created_at.
• Action sub-type defined: An Action struct is created with fields: label, type (enum: navigate, api_call), target, method (nullable), payload (nullable map[string]string). Actions are stored as a JSON column on the notification row.
• GORM annotations correct: All fields carry appropriate GORM tags. actions and meta are stored as serialised JSON columns. Indexes are defined on user_id, is_read, correlation_id, and created_at.
• Auto-migrate verified: Running db.AutoMigrate against a fresh database produces the correct schema for both SQLite and PostgreSQL.
• Type enum validated: The type field is validated against the allowed enum values on creation; invalid values return a descriptive error.
• Unit tests: Tests cover model creation, JSON serialisation/deserialisation of actions and meta, and enum validation.

Definition of Done

• Code implemented following best practices.
• Unit tests written and passing.
• Code reviewed and approved.
• Merged into the main branch.
• Documentation updated (if applicable).
• Deployed to staging/production environment.

Assumptions and Constraints

• Assumption: The project is using GORM as established in the database migration feature. This PBI builds directly on that foundation.
• Constraint: actions and meta must survive a round-trip through both SQLite (TEXT column) and PostgreSQL (JSONB column) without data loss.

Dependencies

No response

Additional Notes

No response