feat: enable document orientation detection for scanned PDFs

- Enable PP-StructureV3's use_doc_orientation_classify feature
- Detect rotation angle from doc_preprocessor_res.angle
- Swap page dimensions (width <-> height) for 90°/270° rotations
- Output PDF now correctly displays landscape-scanned content

Also includes:
- Archive completed openspec proposals
- Add simplify-frontend-ocr-config proposal (pending)
- Code cleanup and frontend simplification

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

frontend/src/hooks/useTaskValidation.ts

@@ -1,5 +1,6 @@
 import { useEffect, useState } from 'react'
 import { useQuery } from '@tanstack/react-query'
+import { AxiosError } from 'axios'
 import { useUploadStore } from '@/store/uploadStore'
 import { useTaskStore } from '@/store/taskStore'
 import { apiClientV2 } from '@/services/apiV2'
@@ -58,7 +59,7 @@ export function useTaskValidation(options?: {
 
   // Handle 404 error - mark as not found and clean up cache
   useEffect(() => {
-    if (error && (error as any)?.response?.status === 404) {
+    if (error && error instanceof AxiosError && error.response?.status === 404) {
       setIsNotFound(true)
       if (taskId) {
         removeFromCache(taskId)