fix: vision slot filters to image-capable + custom models (was relaxing for all providers)

The prior change made the vision slot show every model (image-capable first),
which relaxed the filter for built-in providers too — built-in text-only models
became selectable for Vision. Centralize the vision rule in ModelMenuList:
built-ins must report image input; custom-endpoint models stay selectable (their
capability may be unreported). Image-capable still float first.

tests/setup-dialog-interaction.test.tsx

@@ -172,13 +172,15 @@ describe("setup polish interactions", () => {
 		assert.equal(closed, 0);
 	});
 
-	it("the vision slot lists unknown-capability models (image-capable first, nothing hidden)", async () => {
+	it("the vision slot filters out built-in text-only models (image-capable or custom only)", async () => {
 		await mount({ keyed: true });
 		await click(element('[data-testid="setup-trigger-vision"]'));
-		// The text-only fixture stays selectable in the vision slot: the slot
-		// orders image-capable first but no longer filters, so a custom endpoint
-		// that reports no modality can still be picked for Vision.
-		assert.ok(element('[data-testid="setup-menu-vision"]').textContent?.includes("fixture-text"));
+		// The text-only openrouter fixture is neither image-capable nor a custom-
+		// endpoint model, so the vision slot filters it out (built-ins must report
+		// image input; only custom models stay selectable when capability is unknown).
+		const menu = element('[data-testid="setup-menu-vision"]');
+		assert.ok(!menu.textContent?.includes("fixture-text"));
+		assert.ok(menu.textContent?.includes("No models match."));
 	});
 
 	it("catalog failure uses the approved two-sentence error", async () => {