CD-204: Upgrade ember-cli to 4.12.3

[phndiaye]

What does this PR do?

Update the direct ember-cli dependency to ~4.12.3 and refresh the pnpm lockfile. Keep ember-source and ember-data declarations and resolved versions unchanged.

Related to: CD-204

What are the observable changes?

• Ember CLI resolves to 4.12.3. No application behavior change is intended.
• ember-source and ember-data remain on their existing versions; the separate catalog refactor is out of scope.

🧑‍💻 Developer Heads Up

⚡ Since we are using Ember Octane now:

• Feel free to migrate existing components to Glimmer Components.
• Write new ones exclusively in it.

Useful Resource : Ember Octane vs Classic Cheat Sheet

Good PR checklist

• Title makes sense
• Is against the correct branch
• Only addresses one issue
• Properly assigned
• Added/updated tests
• Added/updated documentation
• Migrated touched components to Glimmer Components
• Properly labeled

Additional Notes

Validation

• pnpm install --lockfile-only --frozen-lockfile --ignore-scripts: passed
• git diff --check: passed
• Build and browser tests were not run locally; CI should validate them.

[linear-code]

CD-204