Add font import for Now, Gotham and Open Sauce One overrides; package fonts for Void

Font import:
- Migration M6 adds user_fonts; files are stored content-addressed under
  the local data dir. New Rust commands inspect, import, list, read and
  remove fonts, refusing WOFF2, collections, variable fonts and
  restricted fsType, and unpacking WOFF1 to plain sfnt.
- Imported fonts register in the render worker as user:<Face> families
  with an italic alias, and are pinned in the frozen render prefs so
  issued invoices can still re-render. Fonts referenced by issued
  invoices are hidden, never deleted.
- Size and tracking compensations tuned for the substitutes apply only
  while the face is not overridden; default output and fingerprint
  goldens are unchanged.
- Settings gets a Fonts section with a licence acknowledgement.

Void packaging:
- Install fonts to /usr/share/fonts/voiced with per-family OFL licences,
  set font_dirs, and add INSTALL/REMOVE scripts that run fc-cache.
  xbps-create carries both scripts (verified in a void-glibc container).
- Fix xbps-create dependency specs in build-xbps.sh.

src/lib/fontImport.ts

@@ -0,0 +1,125 @@
+import type { FontFormat, UserFace } from "../pdf/fonts/userFontStore";
+import { sniffFontFormat, USER_FACES } from "../pdf/fonts/userFontStore";
+import type { RenderPrefsV1 } from "../pdf/model/prefs";
+import { catalogEntry } from "../pdf/templates/catalog";
+
+export { USER_FACES, type UserFace };
+
+/** The three licensed faces and the bundled look-alike each one is drawn with until a font is imported. */
+export const FACE_SUBSTITUTES: Record<UserFace, string> = {
+  Now: "Jost",
+  Gotham: "Montserrat",
+  "Open Sauce One": "Poppins",
+};
+
+/** What the backend found in a font file (src-tauri/src/commands/fonts.rs `FontInspection`). */
+export interface FontInspection {
+  format: "ttf" | "otf";
+  sourceFormat: "ttf" | "otf" | "woff";
+  family: string;
+  subfamily: string;
+  fullName: string;
+  postscriptName: string;
+  weight: number;
+  italic: boolean;
+  fsType: number;
+  numGlyphs: number;
+  hasRupee: boolean;
+  hasBasicLatin: boolean;
+  size: number;
+  sha256: string;
+  warnings: string[];
+}
+
+/** One stored font file (`UserFont`). */
+export interface UserFontRow {
+  id: number;
+  face: UserFace;
+  familyName: string;
+  fullName: string;
+  styleName: string;
+  weight: number;
+  style: "normal" | "italic";
+  sha256: string;
+  fileName: string;
+  format: "ttf" | "otf";
+  size: number;
+  fsType: number;
+  hasRupee: boolean;
+  licenceAckAt: string;
+  importedAt: string;
+  hidden: boolean;
+}
+
+export interface RemoveOutcome {
+  deleted: boolean;
+  hidden: boolean;
+}
+
+export interface ImportMeta {
+  face: UserFace;
+  fileName: string;
+  weight?: number;
+  italic?: boolean;
+  licenceAcknowledged: boolean;
+}
+
+/**
+ * The same magic-byte check the backend makes, to refuse early with a plain message. TTF, OTF and WOFF pass (the
+ * backend unpacks WOFF); the backend stays the authority and repeats every check.
+ */
+export function clientRefusal(bytes: Uint8Array): string | null {
+  const format: FontFormat = sniffFontFormat(bytes);
+  switch (format) {
+    case "ttf":
+    case "otf":
+    case "woff":
+      return null;
+    case "woff2":
+      return "WOFF2 cannot be used: it embeds in a PDF without glyph outlines (invisible text). Import the TTF, OTF or WOFF file instead.";
+    case "ttc":
+      return "Font collections (.ttc) are not supported. Import a single TTF or OTF file.";
+    default:
+      return "This is not a TrueType, OpenType or WOFF font file.";
+  }
+}
+
+export const weightName = (weight: number, italic: boolean): string => {
+  const names: Record<number, string> = { 100: "Thin", 200: "ExtraLight", 300: "Light", 400: "Regular", 500: "Medium", 600: "SemiBold", 700: "Bold", 800: "ExtraBold", 900: "Black" };
+  return `${names[weight] ?? weight}${italic ? " Italic" : ""}`;
+};
+
+/** Visible fonts grouped by face, as the sha256 list `prefs.fonts` carries. */
+export function selectionFrom(fonts: readonly UserFontRow[]): NonNullable<RenderPrefsV1["fonts"]> {
+  const out: NonNullable<RenderPrefsV1["fonts"]> = {};
+  for (const f of fonts) {
+    if (f.hidden) continue;
+    (out[f.face] ??= []).push(f.sha256);
+  }
+  return out;
+}
+
+/**
+ * The prefs to render and issue with: `prefs` plus the imported fonts for the faces this template draws. Fonts for
+ * faces it does not use stay out, so an invoice only pins (and so only protects) the fonts it really uses. The
+ * result is for rendering; keep the clean `prefs` for the page-setup controls and the saved default.
+ */
+export function withUserFonts(prefs: RenderPrefsV1, fonts: readonly UserFontRow[]): RenderPrefsV1 {
+  const { fonts: _drop, ...rest } = prefs;
+  const faces = catalogEntry(prefs.templateId).faces ?? [];
+  const selection = selectionFrom(fonts);
+  const used: NonNullable<RenderPrefsV1["fonts"]> = {};
+  for (const face of faces) {
+    const ids = selection[face];
+    if (ids && ids.length > 0) used[face] = [...ids].sort();
+  }
+  return Object.keys(used).length > 0 ? { ...rest, fonts: used } : rest;
+}
+
+// Settings and the invoice view are separate parts of the UI; this lets the list in one refresh the other.
+const listeners = new Set<() => void>();
+export const onUserFontsChanged = (cb: () => void): (() => void) => {
+  listeners.add(cb);
+  return () => listeners.delete(cb);
+};
+export const notifyUserFontsChanged = (): void => listeners.forEach((cb) => cb());