Derive the version from the Cargo/pubspec manifests

The version string was duplicated across six places. Collapse it to two
ecosystem sources of truth and derive the rest:

- backend/src/web_server.rs: omit the OpenAPI info.version so utoipa fills
  it from CARGO_PKG_VERSION (backend/Cargo.toml); add a test pinning this.
- nix/package.nix: read the version from backend/Cargo.toml via fromTOML.
- nix/frontend.nix: read the version from frontend/pubspec.yaml by splitting
  into lines (a whole-file regex triggers catastrophic backtracking in Nix's
  regex engine).
- frontend/lib/about/about.dart: read the version at runtime via
  package_info_plus instead of a hardcoded constant.

Also drop frontend/pubspec.lock.json: it is unreferenced (Nix's
autoPubspecLock generates its own JSON from pubspec.lock) and was going stale.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/lib/about/about.dart

@@ -1,7 +1,9 @@
 import 'package:flutter/material.dart';
+import 'package:package_info_plus/package_info_plus.dart';
 import 'package:url_launcher/url_launcher.dart';
 
-const _version = '0.1.0';
+// The version is read at runtime from the bundled package metadata
+// (frontend/pubspec.yaml), so it never needs to be hand-edited here.
 const _releaseDate = 'May 28, 2026';
 const _repoUrl = 'https://github.com/rzuasti/oott';
 const _licenseUrl = 'https://www.gnu.org/licenses/agpl-3.0.html';
@@ -28,11 +30,20 @@ class About extends StatelessWidget {
             style: textTheme.bodyLarge,
           ),
           const SizedBox(height: 8),
-          Text(
-            'v$_version - released $_releaseDate',
-            style: textTheme.bodyMedium?.copyWith(
-              color: colorScheme.onSurfaceVariant,
-            ),
+          FutureBuilder<PackageInfo>(
+            future: PackageInfo.fromPlatform(),
+            builder: (context, snapshot) {
+              final version = snapshot.data?.version;
+              final label = version == null
+                  ? 'Released $_releaseDate'
+                  : 'v$version - released $_releaseDate';
+              return Text(
+                label,
+                style: textTheme.bodyMedium?.copyWith(
+                  color: colorScheme.onSurfaceVariant,
+                ),
+              );
+            },
           ),
           const SizedBox(height: 24),
           _SurfaceContainer(

frontend/macos/Flutter/GeneratedPluginRegistrant.swift

@@ -7,12 +7,14 @@ import Foundation
 
 import connectivity_plus
 import encrypter
+import package_info_plus
 import shared_preferences_foundation
 import url_launcher_macos
 
 func RegisterGeneratedPlugins(registry: FlutterPluginRegistry) {
   ConnectivityPlusPlugin.register(with: registry.registrar(forPlugin: "ConnectivityPlusPlugin"))
   EncrypterPlugin.register(with: registry.registrar(forPlugin: "EncrypterPlugin"))
+  FPPPackageInfoPlusPlugin.register(with: registry.registrar(forPlugin: "FPPPackageInfoPlusPlugin"))
   SharedPreferencesPlugin.register(with: registry.registrar(forPlugin: "SharedPreferencesPlugin"))
   UrlLauncherPlugin.register(with: registry.registrar(forPlugin: "UrlLauncherPlugin"))
 }

frontend/pubspec.lock

@@ -384,6 +384,22 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "2.2.0"
+  package_info_plus:
+    dependency: "direct main"
+    description:
+      name: package_info_plus
+      sha256: "16eee997588c60225bda0488b6dcfac69280a6b7a3cf02c741895dd370a02968"
+      url: "https://pub.dev"
+    source: hosted
+    version: "8.3.1"
+  package_info_plus_platform_interface:
+    dependency: transitive
+    description:
+      name: package_info_plus_platform_interface
+      sha256: "202a487f08836a592a6bd4f901ac69b3a8f146af552bbd14407b6b41e1c3f086"
+      url: "https://pub.dev"
+    source: hosted
+    version: "3.2.1"
   path:
     dependency: transitive
     description:
@@ -701,6 +717,14 @@ packages:
       url: "https://pub.dev"
     source: hosted
     version: "1.1.1"
+  win32:
+    dependency: transitive
+    description:
+      name: win32
+      sha256: d7cb55e04cd34096cd3a79b3330245f54cb96a370a1c27adb3c84b917de8b08e
+      url: "https://pub.dev"
+    source: hosted
+    version: "5.15.0"
   xdg_directories:
     dependency: transitive
     description:

frontend/pubspec.yaml

@@ -20,6 +20,7 @@ dependencies:
   fl_chart: ^1.2.0
   google_fonts: ^6.2.1
   url_launcher: ^6.3.0
+  package_info_plus: ^8.0.0
 
 dev_dependencies:
   flutter_test: