fix: enforce public sharing permission checks across all resource types (#21358)

The sharePublic prop in editor components (Knowledge, Tools, Skills,
Prompts, Models) incorrectly included an "|| edit" / "|| write_access"
condition, allowing users with write access to see and use the "Public"
sharing option regardless of their actual public sharing permission.
Additionally, all backend access/update endpoints only verified write
authorization but did not check the corresponding sharing.public_*
permission, allowing direct API calls to bypass frontend restrictions
entirely.
Frontend: removed the edit/write_access bypass from sharePublic in all
five editor components so visibility is gated solely by the user's
sharing.public_* permission or admin role.
Backend: added has_public_read_access_grant checks to the access/update
endpoints in knowledge.py, tools.py, prompts.py, skills.py, models.py,
and notes.py. Public grants are silently stripped when the user lacks
the corresponding permission.
Fixes #21356

src/lib/components/workspace/Models/ModelEditor.svelte

@@ -342,7 +342,7 @@
 		bind:accessGrants
 		accessRoles={preset ? ['read', 'write'] : ['read']}
 		share={$user?.permissions?.sharing?.models || $user?.role === 'admin'}
-		sharePublic={$user?.permissions?.sharing?.public_models || $user?.role === 'admin' || edit}
+		sharePublic={$user?.permissions?.sharing?.public_models || $user?.role === 'admin'}
 		onChange={async () => {
 			if (edit && model?.id) {
 				try {