license: relicense to AGPL-3.0-only with commercial dual-license

- LICENSE -> verbatim GNU AGPL-3.0; add LICENSE-COMMERCIAL.md + SECURITY.md
- CLA -> exclusive-license grant (contributors keep copyright); add README
  anti-rugpull covenant + relicense record
- NOTICE / README / CONTRIBUTING / CLAUDE.md / package.json x5 updated;
  contact routed through GitHub (no email placeholders)
- AGPL section 13 source offer: operator-configurable BACKSPACE_SOURCE_URL +
  build-injected commit; sourceCodeUrl+commit on /api/instance/info;
  SourceCodeLink on login/register/settings/desktop; docs + .env.example updated

packages/desktop/src/recovery.ts

@@ -96,6 +96,8 @@ interface MenuActions {
   onChangeInstance: () => void;
   onCheckForUpdates: () => void;
   onRestartToInstall: () => void;
+  // AGPL-3.0 § 13: open the Corresponding Source of the running instance.
+  onOpenSource: () => void;
   onQuit: () => void;
 }
 
@@ -138,6 +140,7 @@ export function buildTrayMenuTemplate(
   items.push(
     { type: 'separator' },
     { label: 'Change Instance', click: actions?.onChangeInstance },
+    { label: 'Source code (AGPL)', click: actions?.onOpenSource },
     { type: 'separator' },
     { label: 'Quit', click: actions?.onQuit },
   );
@@ -152,6 +155,7 @@ export function buildAppMenuTemplate(
 ): MenuItemConstructorOptions[] {
   const appSubmenu: MenuItemConstructorOptions[] = [
     { role: 'about' },
+    { label: 'Source code (AGPL)', click: () => actions?.onOpenSource?.() },
     { type: 'separator' },
     checkForUpdatesItem(state, () => actions?.onCheckForUpdates?.()),
   ];