优化: 前端扫描文案 i18n + parseStack 抽公共 + alert/confirm 换组件

- 扫描/目录状态文案走 $t（Projects/ProjectDetail，zh-CN+en 同步）
- parseStack 抽公共到 src/utils/project.ts（删两份本地实现）
- 8 处原生 alert/confirm 全换（confirm→ConfirmDialog / alert→Arco Message），控制流语义不变

Sprint 20 审查 ⑥⑦⑧。vue-tsc 0 error，验证 safe 0 issue

src/i18n/en/projectDetail.ts

@@ -48,6 +48,13 @@ export default {
     relocateDir: 'Relocate',
     bindDir: 'Bind Directory',
     dirStatusLabel: 'Directory Status',
+    dirChecking: 'Checking…',
+    dirExists: '✓ Directory exists',
+    dirMissing: '⚠ Directory moved, recommend relocate',
+    dirConflict: 'This directory is already bound to project "{name}"',
+    relocateConfirmRelocate: 'Relocate project directory to:\n{dir}\n\nTech stack will be re-detected. Confirm?',
+    relocateConfirmBind: 'Bind project directory to:\n{dir}\n\nTech stack will be re-detected. Confirm?',
+    relocateFailed: 'Relocate failed: {msg}',
     // Tech stack
     techStackLabel: 'Tech Stack',
   },

src/i18n/en/projects.ts

@@ -26,9 +26,16 @@ export default {
     confirmPurge: 'Permanently delete project "{name}"? Tasks/branches/releases will be physically deleted and cannot be recovered!',
     // New fields
     codeDirLabel: 'Code Directory',
+    codeDirOptionalHint: '(optional, auto-detects tech stack once bound)',
     codeDirPlaceholder: 'Click the button on the right to select project directory',
     selectDir: 'Select Directory',
     clearDir: 'Clear',
+    // AI scan
+    aiScanning: 'AI scanning…',
+    aiScanFill: '🤖 AI scan & autofill',
+    aiScanNoDesc: 'AI could not generate a description, please fill manually',
+    aiScanFailed: 'AI scan failed',
+    dirConflict: 'This directory is already bound to project "{name}"',
     // Status labels (PROJECT_STATUS_LABELS values in constants/project.ts use these keys)
     status: {
       planning: '📐 Planning',