Correct dev port for svelte, closes #3210

Editor assessment

The subject states the defect and its scope completely: the dev port was wrong for svelte in create-tauri-app, with a meaningful create-tauri-app scope and a well-formed closes #3210 footer. The template, the misconfigured value, and the traceability are all present, and the implied symptom (dev server pointing at the wrong port) is directly inferable, so no body is required. The fix type is right, no additional footers appear, and hygiene is clean. A compact, exact message about a template-level configuration error and its correction.