feat(frontend): rename "swap" to "convert" (#3779)

# Motivation

The renaming is requested by the design and product team:

```
It turns out that the word ‘Swap’ might be misleading in our context of ChainFusion conversion. After discussing with 
Stefan, we agreed to stick with the ‘Convert’ naming until we find a better unique one (it's a marketing question tbh).
Can we please update the wording in the modal title and in the ‘Swap fee’ line?”
```

src/frontend/src/lib/i18n/en.json

@@ -379,14 +379,14 @@
 			"fees_explanation": "You need enough $token to cover the smart contract execution fees.",
 			"current_balance": "👉 Current balance:",
 			"review_button": "Review",
-			"convert_button": "Swap",
+			"convert_button": "Convert",
 			"input_reset_button": "Reset input value",
-			"swap_to_token": "Swap $sourceToken → $destinationToken",
+			"swap_to_token": "Convert $sourceToken → $destinationToken",
 			"review": "Review transaction",
 			"available_balance": "Available",
 			"max_balance": "Max",
-			"review_tokens_info_title": "You're swapping",
-			"amount_to_convert": "Amount to swap",
+			"review_tokens_info_title": "You're converting",
+			"amount_to_convert": "Amount to convert",
 			"amount_to_receive": "Amount to receive",
 			"source_network": "Source network",
 			"destination_network": "Destination network",
@@ -537,7 +537,7 @@
 			"estimated_inter_network": "Estimated Inter-network Fee",
 			"estimated_eth": "Estimated Ethereum Fee",
 			"max_fee_eth": "Max fee <small>(likely in &lt; 30 seconds)</small>:",
-			"convert_fee": "Swap fee",
+			"convert_fee": "Conversion fee",
 			"convert_inter_network_fee": "Inter-network fee",
 			"convert_btc_network_fee": "Bitcoin network fee",
 			"zero_fee": "Free",

src/frontend/src/tests/lib/components/convert/ConvertModal.spec.ts

@@ -17,7 +17,7 @@ describe('ConvertModal', () => {
 			context: new Map([[UTXOS_FEE_CONTEXT_KEY, { store: initUtxosFeeStore() }]])
 		});
 
-		const firstStepTitle = 'Swap BTC → ICP';
+		const firstStepTitle = 'Convert BTC → ICP';
 
 		expect(container).toHaveTextContent(firstStepTitle);