## Summary
This PR fixes two issues discovered during testing of the PaddleOCR
async API refactoring:
### 1. PP-OCRv6 returns `ocrResults` instead of `layoutParsingResults`
Models like PP-OCRv6 are pure text recognition models that return
results in `ocrResults.prunedResult.rec_texts` format rather than the
`layoutParsingResults.prunedResult.parsing_res_list` format used by
layout-aware models (PaddleOCR-VL series).
**Changes:**
- `deepdoc/parser/paddleocr_parser.py`: Extract `ocrResults` alongside
`layoutParsingResults` in `_send_request()`, add fallback logic in
`_transfer_to_sections()` and `parse_image()`
- `internal/entity/models/paddleocr.go`: Add `ocrResults` struct and
fallback extraction in Go OCR handler
### 2. Image parsing not integrated into picture chunker
The `parse_image()` method existed in PaddleOCRParser but was never
called from `rag/app/picture.py` (the module that handles image file
uploads). Users configuring PaddleOCR as their layout recognizer would
still get local deepdoc OCR for images.
**Changes:**
- `rag/app/picture.py`: When `layout_recognize` is set to PaddleOCR, use
`PaddleOCROcrModel.parse_image()` instead of local OCR. Falls back
gracefully to local OCR on failure.
## Testing
Verified end-to-end in Docker:
- PaddleOCR-VL-1.6 PDF parsing: ✅ (10 text blocks with bbox)
- PaddleOCR-VL-1.6 image parsing: ✅ (219 chars)
- PP-OCRv6 PDF parsing with ocrResults fallback: ✅ (10 text blocks)
- PP-OCRv6 image parsing with ocrResults fallback: ✅ (136 chars)
## Related PRs
- #15967 (merged) - PaddleOCR async Job API refactoring + new models
- #16086 (merged) - PaddleOCR image parsing support
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