feat: select school terms and smooth refractive Dock motion

mobile/lib/features/school/school_auth_page.dart

@@ -2,6 +2,7 @@ import 'package:flutter/material.dart';
 import 'package:webview_flutter/webview_flutter.dart';
 
 import '../../app/app_controller.dart';
+import '../../domain/school_term.dart';
 import 'school_session.dart';
 
 class SchoolAuthPage extends StatefulWidget {
@@ -18,6 +19,7 @@ class SchoolAuthPage extends StatefulWidget {
 
 class _SchoolAuthPageState extends State<SchoolAuthPage> {
   bool _saving = false;
+  SchoolTerm? _termChoice;
   @override
   void initState() {
     super.initState();
@@ -36,7 +38,9 @@ class _SchoolAuthPageState extends State<SchoolAuthPage> {
     final courses = s.pendingDraft, exams = s.pendingExams;
     final generation = s.pageGeneration;
     final route = ModalRoute.of(context);
-    if (_saving || (courses == null && exams == null)) return;
+    if (s.needsTermSelection || _saving || (courses == null && exams == null)) {
+      return;
+    }
     _saving = true;
     WidgetsBinding.instance.addPostFrameCallback((_) async {
       if (!mounted) {
@@ -102,7 +106,9 @@ class _SchoolAuthPageState extends State<SchoolAuthPage> {
           ),
           IconButton(
             tooltip: '读取当前页面',
-            onPressed: _saving ? null : s.readCurrentPage,
+            onPressed: _saving || s.needsTermSelection
+                ? null
+                : s.readCurrentPage,
             icon: const Icon(Icons.sync_rounded),
           ),
         ],
@@ -123,7 +129,9 @@ class _SchoolAuthPageState extends State<SchoolAuthPage> {
             child: Stack(
               children: [
                 WebViewWidget(controller: s.web),
-                if (s.finding || _saving)
+                if (s.needsTermSelection)
+                  Positioned.fill(child: _termPicker(s)),
+                if (!s.needsTermSelection && (s.finding || _saving))
                   Positioned.fill(
                     child: ColoredBox(
                       color: const Color(0xFFF5F9FE),
@@ -152,4 +160,62 @@ class _SchoolAuthPageState extends State<SchoolAuthPage> {
       ),
     );
   }
+
+  Widget _termPicker(SchoolSession session) {
+    final choices = session.termChoices;
+    final preferred =
+        _termChoice ??
+        session.selectedTerm ??
+        widget.controller.snapshot.schoolTerm ??
+        choices.first;
+    final selected = choices.contains(preferred) ? preferred : choices.first;
+    return Material(
+      color: const Color(0xFFF5F9FE),
+      child: SafeArea(
+        child: Padding(
+          padding: const EdgeInsets.fromLTRB(20, 16, 20, 20),
+          child: Column(
+            crossAxisAlignment: CrossAxisAlignment.stretch,
+            children: [
+              const Text(
+                '选择学校学期',
+                style: TextStyle(fontSize: 22, fontWeight: FontWeight.w700),
+              ),
+              const SizedBox(height: 8),
+              Text(session.requestingExams ? '将读取这个学期的考试安排。' : '将读取这个学期的课程表。'),
+              const SizedBox(height: 12),
+              Expanded(
+                child: ListView.builder(
+                  itemCount: choices.length,
+                  itemBuilder: (context, index) {
+                    final term = choices[index];
+                    final isSelected = term == selected;
+                    return ListTile(
+                      title: Text(term.label),
+                      selected: isSelected,
+                      leading: Icon(
+                        isSelected
+                            ? Icons.radio_button_checked
+                            : Icons.radio_button_off,
+                      ),
+                      onTap: () => setState(() => _termChoice = term),
+                    );
+                  },
+                ),
+              ),
+              const SizedBox(height: 12),
+              FilledButton(
+                onPressed: () => session.selectTerm(selected),
+                child: const Text('导入所选学期'),
+              ),
+              TextButton(
+                onPressed: () => Navigator.of(context).pop(),
+                child: const Text('取消'),
+              ),
+            ],
+          ),
+        ),
+      ),
+    );
+  }
 }