fix: Improve set institution handling for DataKinders

[mrmaloof]

Asana Tasks

EDVISEWEBAPP-4: Replace "DKer must set institution" error message with info level
EDVISEWEBAPP-5: Fix disappearing "successfully set institution" message on Set Institution page

Summary

Adds a variant-based Alert component, migrates former ErrorAlert usage, improves Set Institution loading/success UX, and consolidates Datakinder “set institution” copy on SetInst only (removes PHP constant, query param, and shared Inertia prop).

Changes

• resources/js/Components/Alert.jsx — New Alert with variant: danger | warning | info | success (same props as before: mainMsg, msgDict, excludeValue, className).
• Remove ErrorAlert.jsx — FileUpload, RunInference, Dashboard use <Alert variant="danger" />.
• SetInst.jsx — State-driven submit feedback (no innerHTML); success Alert; router.reload({ only: ['inst_id'] }) after set; warning text hardcoded on this page.
• InstitutionHelper — Remove SET_INST_REQUIRED_MESSAGE; Datakinder without session institution returns ['', ''] from GetInstitution.
• RequireInstitution — Redirect to set-inst without message; JSON returns Institution required.
• HandleInertiaRequests — Drop set_inst_required_message shared prop.
• routes/web.php — SetInst render without message prop.