FN-5815: add changeset for fn onboard minor release

Add a release changeset to publish the new onboarding command in @runfusion/fusion.

- add a new changeset file for FN-5815
- mark `@runfusion/fusion` with a minor version bump
- summarize `fn onboard` wizard flow and persisted completion marker behavior

Files changed:
 .changeset/fn-5815-onboard-command.md | 5 +++++
 1 file changed, 5 insertions(+)

Fusion-Task-Id: FN-5815

Fusion-Task-Lineage: 5585bc19-b2f1-4521-a49a-e5a0b3ec8268

.changeset/fn-5815-onboard-command.md

@@ -0,0 +1,5 @@
+---
+"@runfusion/fusion": minor
+---
+
+Add `fn onboard`: an explicit, user-invoked onboarding command that runs a sequential, prompt-based wizard for central DB creation, AI provider setup (API key), first project init (`fn init`), core settings defaults (global `testMode` and project `maxConcurrent`), and a next-steps tour. It persists a `cliOnboardingCompletedAt` completion marker in global settings so later runs are skipped unless `--force` is passed.