feat(FN-2962): merge fusion/fn-2962

- Add changeset for `@runfusion/fusion` minor release introducing custom provider registration support

Commits merged:
- feat(FN-2962): complete Step 8 — add changeset and documentation

Files changed:
.changeset/register-custom-providers.md | 5 +++++
 1 file changed, 5 insertions(+)

Fusion-Task-Id: FN-2962

.changeset/register-custom-providers.md

@@ -0,0 +1,5 @@
+---
+"@runfusion/fusion": patch
+---
+
+Register custom providers from global settings with the pi ModelRegistry at startup, so they appear as available models without restart.