feat: 旅行伙伴发放与编组、修复退登卡死、优化宽屏布局、加 CI

自动退出登录卡死：_performLogoutAndExit 只 pop() 一层，而解锁/收藏品页是 push
在 HomePage 之上的，退登后被弹回「风险」hub，同时 _loggingOut 仍为 true，
PopScope(canPop:false) + 返回键转圈形成死局。改为 popUntil(isFirst)。

旅行伙伴发不了：它是 ItemKind.Character = 9，与搭档 Partner = 10 是两种东西，
原先收藏品的类型列表 [1,2,3,10,11,12] 里根本没有 9。按客户端实现，角色不走
userItemList(ExportUserItems 不导出 itemKind 9)，而是
upsertUserAll.userCharacterList 的 {characterId, level, awakening, useCount}，
配 isNewCharacterList 一行一字符。新增发放与 5 槽 charaSlot 编组页，
含「把槽 0 复制到其他槽位」，并校验所选角色确为已拥有或本次待发放。

宽屏布局：各页只有 ConstrainedBox 限宽、没有居中容器，1440 窗口下内容贴左、
右侧大片空白。抽出 responsiveBody 统一居中；B50 预览改用按宽度适配
(InteractiveViewer constrained:false + FittedBox fitWidth)，横屏下不再被
contain 缩成中间一小块，导出仍是原始 1762x1850。

CI：.github/workflows/build.yml 先跑 analyze+test 作为门槛，再产出
Windows exe、Android apk、iOS 未签名 ipa(macOS runner，无证书故不可安装)。
README 从 Flutter 模板改写为实际文档，含 path_provider/jni 与 JBR jlink
两个构建环境坑的说明。

.github/workflows/build.yml

@@ -0,0 +1,100 @@
+name: build
+
+on:
+  push:
+    branches: [master]
+    tags: ["v*"]
+  pull_request:
+  workflow_dispatch:
+
+permissions:
+  contents: read
+
+concurrency:
+  group: build-${{ github.workflow }}-${{ github.ref }}
+  cancel-in-progress: true
+
+jobs:
+  checks:
+    name: Analyze & test
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: subosito/flutter-action@v2
+        with:
+          channel: stable
+          cache: true
+      - run: flutter pub get
+      - run: flutter analyze
+      - run: flutter test
+
+  android:
+    name: Android APK
+    needs: checks
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-java@v4
+        with:
+          distribution: temurin
+          java-version: "17"
+      - uses: subosito/flutter-action@v2
+        with:
+          channel: stable
+          cache: true
+      - run: flutter pub get
+      - run: flutter build apk --release
+      - uses: actions/upload-artifact@v4
+        with:
+          name: ichino-android-apk
+          path: build/app/outputs/flutter-apk/app-release.apk
+          if-no-files-found: error
+
+  windows:
+    name: Windows exe
+    needs: checks
+    runs-on: windows-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: subosito/flutter-action@v2
+        with:
+          channel: stable
+          cache: true
+      - run: flutter pub get
+      - run: flutter build windows --release
+      - name: Package runner output
+        shell: pwsh
+        run: |
+          Compress-Archive -Path build\windows\x64\runner\Release\* `
+            -DestinationPath ichino-windows-x64.zip
+      - uses: actions/upload-artifact@v4
+        with:
+          name: ichino-windows-exe
+          path: ichino-windows-x64.zip
+          if-no-files-found: error
+
+  ios:
+    name: iOS unsigned ipa
+    needs: checks
+    runs-on: macos-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: subosito/flutter-action@v2
+        with:
+          channel: stable
+          cache: true
+      - run: flutter pub get
+      # 无证书/描述文件，只能出未签名包：可验证能编译，不能直接装机。
+      - run: flutter build ios --release --no-codesign
+      - name: Package unsigned .ipa
+        run: |
+          set -euo pipefail
+          cd build/ios/iphoneos
+          mkdir -p Payload
+          cp -R Runner.app Payload/
+          zip -qry "$GITHUB_WORKSPACE/ichino-ios-unsigned.ipa" Payload
+      - uses: actions/upload-artifact@v4
+        with:
+          name: ichino-ios-unsigned-ipa
+          path: ichino-ios-unsigned.ipa
+          if-no-files-found: error