feat: add "Add Page Labels" tool to the application

- Introduced a new tool for adding page labels to PDF documents, allowing users to apply Roman numerals, prefixes, and custom numbering ranges.
- Created a new HTML page for the tool with a user-friendly interface for file upload and label rule configuration.
- Implemented logic for handling file uploads, processing PDF files, and applying page labels based on user-defined rules.
- Added necessary types and utility functions for managing page label styles and normalization of start values.
- Updated main application configuration to include the new tool in the navigation.
- Added tests for page label utilities to ensure correct functionality.

src/js/utils/page-labels.ts

@@ -0,0 +1,54 @@
+import type { PageLabelStyleName } from '@/types';
+
+export const PAGE_LABEL_STYLE_OPTIONS = [
+  'DecimalArabic',
+  'LowercaseRoman',
+  'UppercaseRoman',
+  'LowercaseLetters',
+  'UppercaseLetters',
+  'NoLabelPrefixOnly',
+] as const satisfies readonly PageLabelStyleName[];
+
+export type { PageLabelStyleName } from '@/types';
+
+type CpdfLabelStyleSource = {
+  decimalArabic: number;
+  lowercaseRoman: number;
+  uppercaseRoman: number;
+  lowercaseLetters: number;
+  uppercaseLetters: number;
+  noLabelPrefixOnly?: number;
+};
+
+const NO_LABEL_PREFIX_ONLY_FALLBACK = 5 as CpdfLabelStyle;
+
+export function resolvePageLabelStyle(
+  cpdf: CpdfLabelStyleSource,
+  style: PageLabelStyleName
+): CpdfLabelStyle {
+  switch (style) {
+    case 'DecimalArabic':
+      return cpdf.decimalArabic as CpdfLabelStyle;
+    case 'LowercaseRoman':
+      return cpdf.lowercaseRoman as CpdfLabelStyle;
+    case 'UppercaseRoman':
+      return cpdf.uppercaseRoman as CpdfLabelStyle;
+    case 'LowercaseLetters':
+      return cpdf.lowercaseLetters as CpdfLabelStyle;
+    case 'UppercaseLetters':
+      return cpdf.uppercaseLetters as CpdfLabelStyle;
+    case 'NoLabelPrefixOnly':
+      return (
+        (cpdf.noLabelPrefixOnly as CpdfLabelStyle | undefined) ??
+        NO_LABEL_PREFIX_ONLY_FALLBACK
+      );
+  }
+}
+
+export function normalizePageLabelStartValue(value: number): number {
+  if (!Number.isFinite(value)) {
+    return 1;
+  }
+
+  return Math.max(0, Math.floor(value));
+}