copy: improve atprotofans gating hint on upload page (#651)

"gate tracks for supporters" → "offer exclusive tracks to supporters"

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.5 <[e-mail]>

frontend/src/routes/upload/+page.svelte

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 						<span class="gating-disabled-text">
-							want to gate tracks for supporters? <a href="https://atprotofans.com" target="_blank" rel="noopener">set up atprotofans</a>, then enable it in your <a href="/portal">portal</a>
+							want to offer exclusive tracks to supporters? <a href="https://atprotofans.com" target="_blank" rel="noopener">set up atprotofans</a>, then enable it in your <a href="/portal">portal</a>
 						</span>
 					</div>
 				{/if}