Test: release Go-proxy RESTful contract tests verified passing in Go mode (#17468)

### Summary

Aligns Go and Python error codes/messages so both backends honor the
same RESTful API contract, removing implementation-specific error leaks
(MySQL errors, `ValueError`, `AttributeError`, Gin validator format) in
favor of clean business error codes.

**Chat list** — invalid `orderby` now returns code 101 (was: raw Python
`AttributeError` code 100); invalid `page`/`page_size` values fall back
to defaults (was: raw `ValueError`/`ProgrammingError` code 100).

**Dataset create/update/delete** — adds UUID validation (101),
extra-field rejection (101), duplicate-id detection (101), content-type
/ JSON-syntax / object-shape checks (101), and "lacks permission" for
nonexistent datasets (IDOR). Create auto-deduplicates dataset names.
Pagerank updates tolerate a missing ES index. List response includes
`parser_config` and `pagerank`.

**Session list/update** — adds filtering, sorting, and pagination
support. Empty payloads are valid no-ops. Authorization errors map to
code 109.

**Chunk list** — doc object uses Python key names (`chunk_count`,
`dataset_id`, `chunk_method`, run text status). Add validates list
element types.

**Document update** — adds `chunk_method` alias, pydantic-style Field
error messages, metadata index auto-create with refresh, and "These
documents do not belong to dataset" messages. List validates
`metadata_condition` and reports ownership errors for unmatched name/id
filters.

**Search completion** — `kb_ids` ownership failure returns code 102
instead of 109.

Released 31 contract tests from `GO_ONLY_SKIPS` (all verified passing on
both Go and Python backends with real LLM keys).

rag/app/picture.py

@@ -32,7 +32,17 @@ from common.string_utils import clean_markdown_block
 from deepdoc.vision import OCR
 from rag.nlp import attach_media_context, rag_tokenizer, tokenize
 
-ocr = OCR()
+_ocr = None
+
+
+def _get_ocr():
+    """Lazy-init OCR to avoid downloading models at import time (breaks CI
+    collection when the network is unavailable)."""
+    global _ocr
+    if _ocr is None:
+        _ocr = OCR()
+    return _ocr
+
 
 # Gemini supported MIME types
 VIDEO_EXTS = [".mp4", ".mov", ".avi", ".flv", ".mpeg", ".mpg", ".webm", ".wmv", ".3gp", ".3gpp", ".mkv"]
@@ -78,7 +88,7 @@ def chunk(filename, binary, tenant_id, lang, callback=None, **kwargs):
 
         if not txt:
             # Fallback to local deepdoc OCR
-            bxs = ocr(np.array(img))
+            bxs = _get_ocr()(np.array(img))
             txt = "\n".join([t[0] for _, t in bxs if t[0]])
 
         callback(0.4, "Finish OCR: (%s ...)" % txt[:12])