FN-5698: clear OAuth relogin banner after successful login

Clear OAuth re-login banner entries immediately after provider re-authentication.

- add a shared oauth relogin success browser event constant in auth utilities
- dispatch relogin success events from Settings and Model Onboarding OAuth success flows
- update OAuthReloginBanner to listen for relogin success, optimistically clear matching provider rows, and trigger immediate status refresh
- add banner tests covering immediate clearing, refetch behavior, unrelated-provider events, and poll-only behavior
- document the immediate-clear behavior in dashboard docs and add a patch changeset for @runfusion/fusion

Files changed:
 .changeset/fn-5698-relogin-banner-auto-clear.md    |  5 ++
 docs/dashboard-guide.md                            |  4 +
 packages/dashboard/app/auth.ts                     |  1 +
 .../app/components/ModelOnboardingModal.tsx        |  3 +-
 .../app/components/OAuthReloginBanner.tsx          | 70 +++++++++--------
 .../dashboard/app/components/SettingsModal.tsx     |  3 +-
 .../__tests__/OAuthReloginBanner.test.tsx          | 90 ++++++++++++++++++++++
 7 files changed, 144 insertions(+), 32 deletions(-)

Fusion-Task-Id: FN-5698

Fusion-Task-Lineage: 1e2f8055-4f77-4e16-ac15-44891de13f55

docs/dashboard-guide.md

@@ -265,6 +265,10 @@ Push follow-up (when shown):
 
 Branch names are dynamic from merge/audit payloads; the banner is not hardcoded to `main`.
 
+## OAuth Re-login Banner
+
+The global OAuth re-login banner now clears a provider row immediately after that provider successfully re-authenticates (from Settings → Authentication or Model Onboarding), instead of waiting for the next `GET /auth/status` poll interval.
+
 ## Smart Pull
 
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