feat(settings): Open Source Licenses section in System tab (#477)

* feat(licenses): tooling and initial data generation

Adds the maintainer-only generator that produces src/data/licenses.json:
- src-tauri/about.toml + about.hbs: cargo-about config + handlebars template
  for the Rust-side license enumeration
- scripts/generate-licenses.mjs: orchestrator that runs cargo-about and
  license-checker-rseidelsohn (via npx, no devDep), merges the outputs into
  a single per-crate JSON with full license texts, and writes the result to
  src/data/licenses.json

The script is invoked directly with `node scripts/generate-licenses.mjs` —
no npm script wrapper on purpose, since adding one to package.json would
trigger the nix-npm-deps-hash-sync workflow on every push.

Initial generation covers 575 cargo crates + 71 npm packages (646 entries
total, all with full license text bundled, ~1.4 MB JSON).

* feat(licenses): Settings panel UI

Adds a new Open Source Licenses section under Settings → System,
sitting below Contributors. Components:

- LicensesPanel.tsx: search input, curated highlight block of ~10 key
  dependencies (Tauri, React, rodio, symphonia, etc.), TanStack-Virtual
  list of all 600+ entries
- LicenseTextModal.tsx: full-screen-ish modal showing the bundled license
  text plus name/version/license-id badges + repository link
- licensesData.ts: lazy dynamic-import loader (Vite emits the JSON as a
  separate chunk, so the heavy ~1.4 MB payload is only loaded when the
  user actually opens the panel — no runtime fetch, the data is fixed
  into the build artifact)

The panel registers itself in the Settings in-page search index under
the System tab.

* feat(licenses): i18n in 8 locales

Adds the `licenses` namespace (title, intro, highlights, search
placeholder, no-results, loading / load error, no-license-text,
view-source, total line, generated-at) across en, de, fr, nl, zh, nb,
ru, es. License names themselves (MIT, Apache-2.0, GPL-3.0, …) stay
universal and are rendered as-is.

* docs(release): document licenses regeneration step

Adds a Step A.3 to the release SOP describing the maintainer-only
`node scripts/generate-licenses.mjs` workflow, the cargo-about
prerequisite, and explicitly notes why no npm script wrapper exists
(would trigger the nix-npm-deps-hash-sync workflow).

src/utils/licensesData.ts

@@ -0,0 +1,57 @@
+// Lazy loader + types for the bundled `src/data/licenses.json` data.
+//
+// The JSON is generated by `node scripts/generate-licenses.mjs` (maintainer-only)
+// and committed to source. Vite bundles it as a separate JS chunk via dynamic
+// import below, so the heavy ~1–2 MB payload is only loaded when the user
+// actually opens the Open Source Licenses panel — no runtime fetch, the data
+// lives entirely inside the build artifact.
+
+export interface LicenseEntry {
+  name: string;
+  version: string;
+  source: 'npm' | 'cargo';
+  licenses: string[];
+  repository?: string;
+  homepage?: string;
+  description?: string;
+  publisher?: string;
+  licenseText?: string;
+}
+
+export interface LicensesData {
+  generatedAt: string;
+  project: { name: string; version: string };
+  stats: { npm: number; cargo: number; total: number; withFullText: number };
+  entries: LicenseEntry[];
+}
+
+let cache: Promise<LicensesData> | null = null;
+
+export function loadLicensesData(): Promise<LicensesData> {
+  if (cache) return cache;
+  cache = import('../data/licenses.json')
+    .then((mod) => (mod.default ?? mod) as LicensesData)
+    .catch((e) => {
+      cache = null;
+      throw e;
+    });
+  return cache;
+}
+
+/**
+ * Curated list of dependency names shown in the highlight block at the top of
+ * the panel — the user-recognisable backbone of the app. Order matters here;
+ * the panel renders them top-to-bottom as listed.
+ */
+export const HIGHLIGHTED_DEPENDENCIES: Array<{ source: 'npm' | 'cargo'; name: string }> = [
+  { source: 'cargo', name: 'tauri' },
+  { source: 'npm', name: 'react' },
+  { source: 'npm', name: 'zustand' },
+  { source: 'cargo', name: 'rodio' },
+  { source: 'cargo', name: 'symphonia' },
+  { source: 'cargo', name: 'cpal' },
+  { source: 'npm', name: 'axios' },
+  { source: 'npm', name: '@tanstack/react-virtual' },
+  { source: 'npm', name: 'react-i18next' },
+  { source: 'npm', name: 'lucide-react' },
+];