Fix MinerU API sanitized-output lookup and manual chunk tuple handling (#11702)

### What problem does this PR solve?

This PR addresses **two independent issues** encountered when using the
MinerU engine in Ragflow:

1. **MinerU API output path mismatch for non-ASCII filenames**
MinerU sanitizes the root directory name inside the returned ZIP when
the original filename contains non-ASCII characters (e.g., Chinese).
Ragflow's client-side unzip logic assumed the original filename stem and
therefore failed to locate `_content_list.json`.
   This PR adds:

   * root-directory detection
   * fallback lookup using sanitized names
   * a broadened `_read_output` search with a glob fallback
ensuring output files are consistently located regardless of filename
encoding.

2. **Chunker crash due to tuple-structure mismatch in manual mode**
Some parsers (e.g., MinerU / Docling) return **2-tuple sections**, but
Ragflow’s chunker expects **3-tuple sections**, leading to:
   `ValueError: not enough values to unpack (expected 3, got 2)`
This PR normalizes all sections to a uniform structure `(text, layout,
positions)`:

   * parse position tags when present
   * default to empty positions when missing
     preserving backward compatibility and preventing crashes.

### Type of change

* [x] Bug Fix (non-breaking change which fixes an issue)


[#11136](https://github.com/infiniflow/ragflow/issues/11136)
[#11700](https://github.com/infiniflow/ragflow/issues/11700)
[#11620](https://github.com/infiniflow/ragflow/issues/11620)
[#11701](https://github.com/infiniflow/ragflow/pull/11701)

we need your help [yongtenglei](https://github.com/yongtenglei)

---------

Co-authored-by: Kevin Hu <kevinhu.sh@gmail.com>

rag/app/manual.py

@@ -219,23 +219,27 @@ def chunk(filename, binary=None, from_page=0, to_page=100000,
         )
 
         def _normalize_section(section):
-            # pad section to length 3: (txt, sec_id, poss)
-            if len(section) == 1:
+            # Pad/normalize to (txt, layout, positions)
+            if not isinstance(section, (list, tuple)):
+                section = (section, "", [])
+            elif len(section) == 1:
                 section = (section[0], "", [])
             elif len(section) == 2:
                 section = (section[0], "", section[1])
-            elif len(section) != 3:
-                raise ValueError(f"Unexpected section length: {len(section)} (value={section!r})")
+            else:
+                section = (section[0], section[1], section[2])
 
             txt, layoutno, poss = section
             if isinstance(poss, str):
                 poss = pdf_parser.extract_positions(poss)
-                first = poss[0]          # tuple: ([pn], x1, x2, y1, y2)
-                pn = first[0]
-
-                if isinstance(pn, list):
-                    pn = pn[0]           # [pn] -> pn
+                if poss:
+                    first = poss[0]  # tuple: ([pn], x1, x2, y1, y2)
+                    pn = first[0]
+                    if isinstance(pn, list) and pn:
+                        pn = pn[0]  # [pn] -> pn
                     poss[0] = (pn, *first[1:])
+            if not poss:
+                poss = []
 
             return (txt, layoutno, poss)