fix(domain): migrate issue component to text

[DoDiODev]

Summary

Migrate the domain-layer issues.component column to TEXT.

The existing 2024 migration targets the non-existent plural column issues.components, so databases upgraded through that migration can retain issues.component as VARCHAR(255) even though the current domain model declares it as text. This can truncate or reject component values longer than 255 characters.

Scope

• Add a new immutable follow-up migration that changes issues.component to TEXT through the database-neutral DAL.
• Register the migration in the core migration list.
• Add a regression test covering the table, singular column name, target type, migration metadata, and registration.
• Keep the already published 2024 migration unchanged.

Excluded

This PR intentionally contains no Jira tool-layer changes, plugin changes, infrastructure updates, or fork-specific artifacts.

Testing

• make build
• cd backend && go test ./core/models/... -count=1
• cd backend && make migration-script-lint
• git diff --check upstream/main...HEAD

The change set and manual gate were reviewed and approved before submission.

Rollback

Reverting this commit before release removes the new migration. Once the migration has shipped and executed, it should remain immutable; any later schema adjustment should use a new follow-up migration rather than modifying this one.

Dependencies

None. This PR is based directly on apache/devlake:main.