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/components/LicenseTextModal.tsx

@@ -0,0 +1,132 @@
+import { useEffect } from 'react';
+import { createPortal } from 'react-dom';
+import { X, ExternalLink } from 'lucide-react';
+import { useTranslation } from 'react-i18next';
+import { open as openExternal } from '@tauri-apps/plugin-shell';
+import type { LicenseEntry } from '../utils/licensesData';
+
+interface Props {
+  entry: LicenseEntry | null;
+  onClose: () => void;
+}
+
+export default function LicenseTextModal({ entry, onClose }: Props) {
+  const { t } = useTranslation();
+
+  useEffect(() => {
+    if (!entry) return;
+    const onKey = (e: KeyboardEvent) => {
+      if (e.key === 'Escape') onClose();
+    };
+    window.addEventListener('keydown', onKey);
+    return () => window.removeEventListener('keydown', onKey);
+  }, [entry, onClose]);
+
+  if (!entry) return null;
+
+  const repoLink = entry.repository || entry.homepage;
+
+  return createPortal(
+    <div
+      className="modal-overlay"
+      onClick={onClose}
+      role="dialog"
+      aria-modal="true"
+      style={{ alignItems: 'center', paddingTop: 0 }}
+    >
+      <div
+        className="modal-content"
+        onClick={(e) => e.stopPropagation()}
+        style={{
+          maxWidth: '760px',
+          width: '92vw',
+          maxHeight: '82vh',
+          display: 'flex',
+          flexDirection: 'column',
+        }}
+      >
+        <button className="modal-close" onClick={onClose} aria-label={t('common.close')}>
+          <X size={18} />
+        </button>
+        <div style={{ marginBottom: '0.5rem', paddingRight: '2rem' }}>
+          <h3 style={{ margin: 0, fontFamily: 'var(--font-display)', fontSize: '1.05rem' }}>
+            {entry.name} <span style={{ color: 'var(--text-muted)', fontWeight: 400 }}>{entry.version}</span>
+          </h3>
+          <div
+            style={{
+              display: 'flex',
+              gap: '8px',
+              alignItems: 'center',
+              flexWrap: 'wrap',
+              marginTop: '0.4rem',
+              fontSize: '0.78rem',
+            }}
+          >
+            {entry.licenses.map((lid) => (
+              <span
+                key={lid}
+                style={{
+                  background: 'var(--bg-card)',
+                  border: '1px solid var(--border)',
+                  borderRadius: '10px',
+                  padding: '1px 8px',
+                  color: 'var(--text-primary)',
+                }}
+              >
+                {lid}
+              </span>
+            ))}
+            <span
+              style={{
+                color: 'var(--text-muted)',
+                textTransform: 'uppercase',
+                fontSize: '0.7rem',
+                letterSpacing: '0.04em',
+              }}
+            >
+              {entry.source}
+            </span>
+            {repoLink && (
+              <button
+                onClick={() => openExternal(repoLink)}
+                className="btn btn-ghost"
+                style={{
+                  padding: '2px 8px',
+                  fontSize: '0.78rem',
+                  display: 'inline-flex',
+                  alignItems: 'center',
+                  gap: '4px',
+                }}
+              >
+                <ExternalLink size={12} /> {t('licenses.viewSource')}
+              </button>
+            )}
+          </div>
+          {entry.description && (
+            <p style={{ color: 'var(--text-muted)', marginTop: '0.6rem', marginBottom: 0, fontSize: '0.85rem' }}>
+              {entry.description}
+            </p>
+          )}
+        </div>
+        <div
+          style={{
+            background: 'var(--bg-card)',
+            border: '1px solid var(--border)',
+            borderRadius: 'var(--radius-sm)',
+            padding: '12px 14px',
+            overflow: 'auto',
+            flex: 1,
+            fontFamily: 'var(--font-mono, ui-monospace, monospace)',
+            fontSize: '0.78rem',
+            whiteSpace: 'pre-wrap',
+            color: 'var(--text-primary)',
+            lineHeight: 1.5,
+          }}
+        >
+          {entry.licenseText || t('licenses.noLicenseText')}
+        </div>
+      </div>
+    </div>,
+    document.body,
+  );
+}