feat(wallpaper-generator): add device wallpaper generation package

Add new @manacore/wallpaper-generator package for creating device
wallpapers from QR codes and images.

Features:
- 30 device presets (phones, tablets, desktops)
- 3 layout types (center, corner, pattern)
- 5 gradient presets + solid color backgrounds
- Browser (Canvas) and Node.js (Sharp) renderers
- Svelte WallpaperModal UI component

Integrations:
- @manacore/qr-export: toWallpaper() function
- @manacore/spiral-db: toWallpaper() function
- QRExportModal: "Als Wallpaper" button

Also includes the full @manacore/qr-export package which was
previously untracked.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

packages/qr-export/src/encoder.test.ts

@@ -0,0 +1,153 @@
+import { describe, it, expect } from 'vitest';
+import { encode, decode, estimateSize, willFitInQR, MANA_QR_PREFIX } from './encoder';
+import { createManaQRExport, contact, event, todo } from './builder';
+import type { ManaQRExport } from './types';
+
+describe('encoder', () => {
+	const sampleExport: ManaQRExport = {
+		v: 1,
+		ts: 1708185600,
+		u: {
+			n: 'Till',
+			z: 'Europe/Berlin',
+			l: 'de',
+			w: 'Berlin',
+		},
+		c: [
+			{ n: 'Mama', p: '+491701234567', r: 1 },
+			{ n: 'Papa', p: '+491707654321', r: 1 },
+		],
+		e: [
+			{ t: 'Zahnarzt', s: 1708272000, d: 60, l: 'Praxis Dr. Weber' },
+			{ t: 'Team Meeting', s: 1708358400, d: 30 },
+		],
+		t: [
+			{ t: 'Steuererklärung abgeben', p: 1, d: 14 },
+			{ t: 'Backup machen', p: 3 },
+		],
+	};
+
+	describe('encode', () => {
+		it('should encode data with correct prefix', () => {
+			const result = encode(sampleExport);
+
+			expect(result.data.startsWith(MANA_QR_PREFIX)).toBe(true);
+			expect(result.size).toBeGreaterThan(0);
+		});
+
+		it('should report fitsInQR correctly for small data', () => {
+			const result = encode(sampleExport);
+
+			expect(result.fitsInQR).toBe(true);
+			expect(result.size).toBeLessThan(2500);
+		});
+
+		it('should compress data significantly', () => {
+			const jsonSize = JSON.stringify(sampleExport).length;
+			const result = encode(sampleExport);
+
+			// Encoded should be smaller than raw JSON
+			expect(result.size).toBeLessThan(jsonSize);
+		});
+	});
+
+	describe('decode', () => {
+		it('should decode encoded data correctly', () => {
+			const encoded = encode(sampleExport);
+			const decoded = decode(encoded.data);
+
+			expect(decoded.success).toBe(true);
+			if (decoded.success) {
+				expect(decoded.data.u.n).toBe('Till');
+				expect(decoded.data.c).toHaveLength(2);
+				expect(decoded.data.e).toHaveLength(2);
+				expect(decoded.data.t).toHaveLength(2);
+			}
+		});
+
+		it('should fail for invalid prefix', () => {
+			const result = decode('INVALID:xyz');
+
+			expect(result.success).toBe(false);
+			if (!result.success) {
+				expect(result.error).toBe('INVALID_PREFIX');
+			}
+		});
+
+		it('should fail for invalid base64', () => {
+			const result = decode(MANA_QR_PREFIX + '!!!invalid!!!');
+
+			expect(result.success).toBe(false);
+			if (!result.success) {
+				expect(result.error).toBe('INVALID_BASE64');
+			}
+		});
+	});
+
+	describe('roundtrip', () => {
+		it('should preserve all data through encode/decode', () => {
+			const encoded = encode(sampleExport);
+			const decoded = decode(encoded.data);
+
+			expect(decoded.success).toBe(true);
+			if (decoded.success) {
+				expect(decoded.data).toEqual(sampleExport);
+			}
+		});
+	});
+
+	describe('estimateSize', () => {
+		it('should estimate size within reasonable range', () => {
+			const estimated = estimateSize(sampleExport);
+			const actual = encode(sampleExport).size;
+
+			// Estimate should be within 50% of actual
+			expect(estimated).toBeGreaterThan(actual * 0.5);
+			expect(estimated).toBeLessThan(actual * 1.5);
+		});
+	});
+
+	describe('willFitInQR', () => {
+		it('should return true for small data', () => {
+			expect(willFitInQR(sampleExport)).toBe(true);
+		});
+	});
+});
+
+describe('builder', () => {
+	it('should build export with fluent API', () => {
+		const result = createManaQRExport()
+			.user({ n: 'Test', z: 'UTC', l: 'en' })
+			.addContact(contact('Alice', '+1234567890', 1))
+			.addEvent(event('Meeting', new Date('2024-02-20T10:00:00Z'), 60))
+			.addTodo(todo('Task 1', 1, 7))
+			.build();
+
+		expect(result.v).toBe(1);
+		expect(result.u.n).toBe('Test');
+		expect(result.c).toHaveLength(1);
+		expect(result.e).toHaveLength(1);
+		expect(result.t).toHaveLength(1);
+	});
+
+	it('should encode to valid QR string', () => {
+		const result = createManaQRExport()
+			.userName('Test')
+			.timezone('UTC')
+			.addContact({ n: 'Bob', r: 3 })
+			.encode();
+
+		expect(result.data.startsWith(MANA_QR_PREFIX)).toBe(true);
+		expect(result.fitsInQR).toBe(true);
+	});
+
+	it('should estimate size correctly', () => {
+		const builder = createManaQRExport().userName('Test').addContact({ n: 'Alice', r: 1 });
+
+		const estimated = builder.estimateSize();
+		const _actual = builder.encode().size;
+
+		expect(estimated).toBeGreaterThan(0);
+		expect(builder.willFit()).toBe(true);
+	});
+});