feat: 5-issue fix — OCR image parse bug + Vue frontend feature parity + streaming UX

Fix 1 (CRITICAL): file_parser.py suffix normalization ".jpg", api_server.py Path.suffix
Fix 2: Sidebar version history download, ProcessSection replaces old components
Fix 3: OCR content/position layer structured logging in agent/nodes.py
Fix 4: collapsible process sections with per-section stream routing + auto-fold
Fix 5: agent_complete total_duration_ms, SummaryCard duration display

- backend/file_parser.py: normalize suffix to always include leading dot
- api_server.py: step_index in node_start, total_duration_ms in agent_complete
- agent/nodes.py: _log_ocr_layers() for [内容层]/[位置层]/[合并] logging
- frontend: ProcessSection.vue (NEW), chat.ts sections model, Sidebar versions
- CLAUDE.md: updated component list and v6 changelog

frontend/src/api/client.ts

@@ -28,11 +28,12 @@ export interface AgentCompleteData {
   error_msg: string
   natural_explanation: string
   retry_count: number
+  total_duration_ms: number
   ocr_extraction_result: any
 }
 
 export interface SSECallbacks {
-  onNodeStart?: (data: { node: string; label: string }) => void
+  onNodeStart?: (data: { node: string; label: string; step_index: number }) => void
   onNodeComplete?: (data: { node: string; label: string; detail: string }) => void
   onStreamToken?: (data: { text: string; type: string }) => void
   onAgentComplete?: (data: AgentCompleteData) => void