feat: implement English Style Converter

- SvelteKit project scaffolded with TypeScript
- Type definitions for Style, StyleCategory, ConversionRequest, ConversionResponse, LLMConfig
- Style definitions with 6 categories and 25 sub-styles
- Intensity mapping (1-5) with prompt modifier placeholders
- LLM client using OpenAI-compatible API (Ollama default)
- POST /api/convert endpoint with input validation
- Animated loading modal with per-letter animations
- Main page UI with category/style selectors, intensity slider
- Copy to clipboard, collapsible prompt display
- Vitest tests for styles, LLM prompt building, and API validation
- Environment configuration for LLM settings

src/lib/llm.test.ts

@@ -0,0 +1,34 @@
+import { describe, it, expect } from 'vitest';
+import { buildSystemPrompt, buildUserMessage } from '$lib/llm';
+
+describe('buildSystemPrompt', () => {
+	it('fills in {style} placeholder from intensity instruction', () => {
+		const result = buildSystemPrompt(
+			'Rewrite in a sarcastic, snarky tone with biting wit',
+			'rewrite strongly in a {style} style'
+		);
+		expect(result).toContain('rewrite strongly in a Rewrite in a sarcastic, snarky tone with biting wit style');
+		expect(result).not.toContain('{style}');
+	});
+
+	it('includes the style modifier on its own line', () => {
+		const result = buildSystemPrompt('some modifier', 'lightly hint at a {style} tone');
+		expect(result).toContain('some modifier');
+	});
+
+	it('includes the core instruction text', () => {
+		const result = buildSystemPrompt('test', 'rewrite with a {style} tone');
+		expect(result).toContain('You are an expert English style converter');
+		expect(result).toContain('Output ONLY the converted text');
+	});
+});
+
+describe('buildUserMessage', () => {
+	it('returns the text as-is', () => {
+		expect(buildUserMessage('Hello world')).toBe('Hello world');
+	});
+
+	it('preserves whitespace', () => {
+		expect(buildUserMessage('  spaced  ')).toBe('  spaced  ');
+	});
+});