Add bundled TTF fonts, page geometry, column allocator and render model

Static TTF fonts (IBM Plex Sans/Mono, Noto Devanagari/Kannada) with a
fontkit-generated manifest, a verifier and OFL licences. Every family
registers a normal and italic source so fallback stacks cannot throw.
Adds A4/Letter geometry with margin presets, an exact column allocator,
deterministic Indian-grouping money and date formatting, text sanitising
and a pure buildRenderModel.

src/pdf/fonts/register.ts

@@ -0,0 +1,85 @@
+import { Font } from "@react-pdf/renderer";
+import { FONT_MANIFEST } from "./manifest";
+
+/** Every stack ends here: Latin and the rupee sign from Plex, then the Indic scripts. */
+export const FONT_STACK: readonly string[] = [
+  "IBM Plex Sans",
+  "Noto Sans Devanagari",
+  "Noto Sans Kannada",
+];
+
+/** `[primary, ...tail]` without duplicates, for a style's fontFamily. */
+export function stack(primary: string): string[] {
+  return [primary, ...FONT_STACK.filter((f) => f !== primary)];
+}
+
+let registered = false;
+
+/**
+ * Registers every bundled family from the manifest. Idempotent; never call Font.reset(), the fonts
+ * would not load again.
+ *
+ * `base` is a URL prefix in the app ("/fonts") and a directory under Node (tests). Only static TTF is
+ * used: WOFF2 embeds glyphs without outlines (invisible text) and variable fonts embed only their
+ * default instance.
+ */
+export function registerBundledFonts(base: string): void {
+  if (registered) return;
+  registered = true;
+
+  for (const fam of FONT_MANIFEST.families) {
+    const sources: { src: string; fontWeight: number; fontStyle: "normal" | "italic" }[] = [];
+    const weights = new Set<number>();
+    for (const font of fam.fonts) {
+      weights.add(font.weight);
+      sources.push({
+        src: `${base}/${fam.folder}/${font.file}`,
+        fontWeight: font.weight,
+        fontStyle: font.style,
+      });
+    }
+    // react-pdf resolves every family in a fallback stack with the node's own style and throws for
+    // a family that has no italic, so any weight without a real italic reuses its upright file.
+    for (const weight of weights) {
+      if (sources.some((s) => s.fontWeight === weight && s.fontStyle === "italic")) continue;
+      const upright = sources.find((s) => s.fontWeight === weight && s.fontStyle === "normal");
+      if (upright) sources.push({ ...upright, fontStyle: "italic" });
+    }
+    Font.register({ family: fam.family, fonts: sources });
+  }
+
+  // The default hyphenation inserts "-" into e-mail addresses, URLs and identifiers.
+  Font.registerHyphenationCallback((word) => [word]);
+}
+
+const MIN_FONT_BYTES = 10 * 1024;
+
+function hasTrueTypeMagic(b: Uint8Array): boolean {
+  if (b.length < 4) return false;
+  if (b[0] === 0 && b[1] === 1 && b[2] === 0 && b[3] === 0) return true;
+  return String.fromCharCode(b[0], b[1], b[2], b[3]) === "true";
+}
+
+/**
+ * Fetches every bundled font and returns a list of problems (empty when all are fine). Tauri answers
+ * an unknown path with index.html and HTTP 200, so the response bytes must be checked, not the status.
+ */
+export async function preflightFonts(
+  fetchBytes: (url: string) => Promise<Uint8Array>,
+  base: string,
+): Promise<string[]> {
+  const problems: string[] = [];
+  for (const fam of FONT_MANIFEST.families) {
+    for (const font of fam.fonts) {
+      const url = `${base}/${fam.folder}/${font.file}`;
+      try {
+        const bytes = await fetchBytes(url);
+        if (!hasTrueTypeMagic(bytes)) problems.push(`${url}: not a TrueType font`);
+        else if (bytes.length <= MIN_FONT_BYTES) problems.push(`${url}: only ${bytes.length} bytes`);
+      } catch (err) {
+        problems.push(`${url}: ${err instanceof Error ? err.message : String(err)}`);
+      }
+    }
+  }
+  return problems;
+}