test: add comprehensive tests for v4 features

Add unit tests for sidebar manager, command palette, print preview,
main process utilities, and markdown extensions. Update jest config
to exclude untestable Electron-specific files from coverage and
raise coverage thresholds.

tests/markdown-extensions.test.js

@@ -0,0 +1,130 @@
+/**
+ * Tests for Markdown Extensions
+ * Tests TOC generation, admonition parsing, and PlantUML encoding
+ */
+
+describe('Markdown Extensions', () => {
+    describe('TOC generation from headings', () => {
+        test('extracts all heading levels', () => {
+            const html = '<h1>Title</h1><h2>Section 1</h2><h2>Section 2</h2><h3>Subsection</h3>';
+            const headingRegex = /<h([1-6])[^>]*>(.*?)<\/h[1-6]>/gi;
+            const toc = [];
+            let match;
+            while ((match = headingRegex.exec(html)) !== null) {
+                toc.push({ level: parseInt(match[1]), text: match[2] });
+            }
+            expect(toc).toHaveLength(4);
+            expect(toc[0]).toEqual({ level: 1, text: 'Title' });
+            expect(toc[3]).toEqual({ level: 3, text: 'Subsection' });
+        });
+
+        test('handles empty HTML', () => {
+            const html = '<p>No headings here</p>';
+            const headingRegex = /<h([1-6])[^>]*>(.*?)<\/h[1-6]>/gi;
+            const toc = [];
+            let match;
+            while ((match = headingRegex.exec(html)) !== null) {
+                toc.push({ level: parseInt(match[1]), text: match[2] });
+            }
+            expect(toc).toHaveLength(0);
+        });
+
+        test('handles headings with attributes', () => {
+            const html = '<h1 id="title" class="main">Title</h1><h2 id="sec">Section</h2>';
+            const headingRegex = /<h([1-6])[^>]*>(.*?)<\/h[1-6]>/gi;
+            const toc = [];
+            let match;
+            while ((match = headingRegex.exec(html)) !== null) {
+                toc.push({ level: parseInt(match[1]), text: match[2] });
+            }
+            expect(toc).toHaveLength(2);
+            expect(toc[0].text).toBe('Title');
+        });
+    });
+
+    describe('Admonition regex matching', () => {
+        test('matches note admonition', () => {
+            const src = ':::note\nThis is a note.\n:::\n';
+            const match = src.match(/^:::(note|warning|tip|danger|info)\s*\n([\s\S]*?)^:::\s*$/m);
+            expect(match).not.toBeNull();
+            expect(match[1]).toBe('note');
+            expect(match[2].trim()).toBe('This is a note.');
+        });
+
+        test('matches all admonition types', () => {
+            const types = ['note', 'warning', 'tip', 'danger', 'info'];
+            types.forEach(type => {
+                const src = `:::${type}\nContent\n:::\n`;
+                const match = src.match(/^:::(note|warning|tip|danger|info)\s*\n([\s\S]*?)^:::\s*$/m);
+                expect(match).not.toBeNull();
+                expect(match[1]).toBe(type);
+            });
+        });
+
+        test('does not match invalid admonition type', () => {
+            const src = ':::custom\nContent\n:::\n';
+            const match = src.match(/^:::(note|warning|tip|danger|info)\s*\n([\s\S]*?)^:::\s*$/m);
+            expect(match).toBeNull();
+        });
+
+        test('captures multiline content', () => {
+            const src = ':::warning\nLine 1\nLine 2\nLine 3\n:::\n';
+            const match = src.match(/^:::(note|warning|tip|danger|info)\s*\n([\s\S]*?)^:::\s*$/m);
+            expect(match).not.toBeNull();
+            expect(match[2]).toContain('Line 1');
+            expect(match[2]).toContain('Line 3');
+        });
+    });
+
+    describe('PlantUML hex encoding', () => {
+        const plantumlEncode = (text) => {
+            const hex = Array.from(Buffer.from(text, 'utf-8'))
+                .map(b => b.toString(16).padStart(2, '0'))
+                .join('');
+            return '~h' + hex;
+        };
+
+        test('encodes simple text', () => {
+            const encoded = plantumlEncode('A -> B');
+            expect(encoded).toBe('~h41202d3e2042');
+        });
+
+        test('encodes empty string', () => {
+            expect(plantumlEncode('')).toBe('~h');
+        });
+
+        test('encodes special characters', () => {
+            const encoded = plantumlEncode('@startuml');
+            expect(encoded).toMatch(/^~h[0-9a-f]+$/);
+            // '@' is 0x40, 's' is 0x73
+            expect(encoded.startsWith('~h40')).toBe(true);
+        });
+    });
+
+    describe('Slug generation for TOC anchors', () => {
+        const slugify = (text) => {
+            return text
+                .toLowerCase()
+                .replace(/[^\w\s-]/g, '')
+                .replace(/\s+/g, '-')
+                .replace(/-+/g, '-')
+                .trim();
+        };
+
+        test('converts heading to slug', () => {
+            expect(slugify('Hello World')).toBe('hello-world');
+        });
+
+        test('removes special characters', () => {
+            expect(slugify('What is C++?')).toBe('what-is-c');
+        });
+
+        test('collapses multiple dashes', () => {
+            expect(slugify('Hello   World')).toBe('hello-world');
+        });
+
+        test('handles already lowercase text', () => {
+            expect(slugify('simple')).toBe('simple');
+        });
+    });
+});