docs: clarify v3 self-hosting wording and fix a comma splice

Make the server-changes note user-facing and self-hosted-scoped (drop the
internal "v3 engine" term and the ambiguous "instances"), and use a semicolon
instead of a comma splice in the migration guide.

Author: ericallam

.server-changes/remove-v3-engine.md

@@ -3,4 +3,4 @@ area: webapp
 type: breaking
 ---
 
-Removed support for the end-of-life v3 engine. 4.5.0 is the last version we officially support for running v3, so instances or projects still on v3 must stay on 4.5.0 or upgrade to v4; v3 triggers, batch triggers, reschedules, and deploys now return a clear upgrade message instead of running.
+Trigger.dev v3 is no longer supported. For self-hosted deployments, 4.5.0 is the last version we officially support for running v3; stay on 4.5.0 or upgrade to v4. v3 triggers, batch triggers, reschedules, and deploys now return a clear upgrade message instead of running.

docs/migrating-from-v3.mdx

@@ -14,7 +14,7 @@ Trigger.dev v3 is end of life. v4 is stable, fully supported, and recommended fo
 - On Trigger.dev Cloud, v3 has been shut down: v3 triggers and deploys no longer run.
 - If you self-host, 4.5.0 is the last version we officially support for running v3. Stay on 4.5.0 or upgrade to v4; 4.5.1 and later reject v3 triggers, batch triggers, and deploys with an upgrade message.
 
-**What you need to do:** Migrate to v4. The migration takes about 2 minutes, follow the steps on this page below. If you have questions or need help, [contact us](https://trigger.dev/contact) or reach out in our [Discord](https://trigger.dev/discord).
+**What you need to do:** Migrate to v4. The migration takes about 2 minutes; follow the steps below. If you have questions or need help, [contact us](https://trigger.dev/contact) or reach out in our [Discord](https://trigger.dev/discord).
 
 </Warning>