✨ feat(vscode): 摘修复识别 alembic 迁移，接不上发布分支链的高亮禁用不可摘

按 writing-alembic-migrations 的规矩判断：迁移的前任必须已在发布分支上，
且发布分支上该前任不能已有别的后继；根迁移接不上已有链、删迁移会断链也不可摘。
列表里带迁移的提交打「迁移」角标，不可摘的高亮警告色、禁用勾选并写明原因；
确认接口再校验一遍，绕过前端也摘不进去。

Claude-Session: https://claude.ai/code/session_01QWxLb6X8Vd2G5vHnp6R7qm

vscode/webview-ui/src/lib/cherryPickView.test.ts

@@ -1,6 +1,6 @@
 import type { ReleaseCommitGroup } from './messages'
 import { describe, expect, it } from 'vitest'
-import { filterCherryPickGroups, uniqueAuthors } from './cherryPickView'
+import { filterCherryPickGroups, pickableShas, uniqueAuthors } from './cherryPickView'
 
 const groups: ReleaseCommitGroup[] = [
   {
@@ -35,3 +35,14 @@ describe('uniqueAuthors', () => {
     expect(uniqueAuthors(groups)).toEqual(['cruldra', 'chehongweo'])
   })
 })
+
+describe('pickableShas', () => {
+  it('带不兼容迁移的提交不能勾；兼容的迁移照常', () => {
+    const commits = [
+      { sha: 'a', subject: 'ok', author: 'x', date: '', body: '' },
+      { sha: 'b', subject: 'mig ok', author: 'x', date: '', body: '', migration: { files: ['alembic/versions/0002.py'] } },
+      { sha: 'c', subject: 'mig bad', author: 'x', date: '', body: '', migration: { files: ['alembic/versions/0003.py'], blocked: '上游迁移 0002 不在 release/x' } },
+    ]
+    expect(pickableShas(commits)).toEqual(['a', 'b'])
+  })
+})