Add plan_name_uid columns to referencing tables

Objective

Add new plan_name_uid and hosted_plan_name_uid columns to all tables that reference the plans table and create backfill migrations.

Prerequisites

• Plans table enum column completed (#571419 (closed))

Scope

Add new columns to tables that reference plans:

• plan_limits → add plan_name_uid
• gitlab_subscriptions → add hosted_plan_name_uid
• gitlab_subscription_histories → add hosted_plan_name_uid
• ci_pending_builds → add plan_name_uid (if applicable)
• instance_type_ci_runners → add plan_name_uid (if applicable)
• project_type_ci_runners → add plan_name_uid (if applicable)

Tasks

• Create migrations to add new columns to all referencing tables
• Add indexes on new columns for performance

Migration Strategy

For each table:

1. Add new *_name_uid column as nullable integer
2. Add index on new column

Acceptance Criteria

• All referencing tables have new *_name_uid columns
• Indexes created for performance
• No data loss during migration
• Migrations are reversible
• Edge cases handled appropriately

References

• Parent Epic: Convert `plans` table to be hard-coded in appli... (&19409)
• Original Issue: #519892 (closed)
• Previous: #571419 (closed)