Add universal document decoder with multi-format support (#705)

Add universal document decoder with multi-format support
using 'unstructured'.

New universal decoder service powered by the unstructured
library, handling DOCX, XLSX, PPTX, HTML, Markdown, CSV, RTF,
ODT, EPUB and more through a single service. Tables are preserved
as HTML markup for better downstream extraction. Images are
stored in the librarian but excluded from the text
pipeline. Configurable section grouping strategies
(whole-document, heading, element-type, count, size) for non-page
formats. Page-based formats (PDF, PPTX, XLSX) are automatically
grouped by page.

All four decoders (PDF, Mistral OCR, Tesseract OCR, universal)
now share the "document-decoder" ident so they are
interchangeable.  PDF-only decoders fetch document metadata to
check MIME type and gracefully skip unsupported formats.

Librarian changes: removed MIME type whitelist validation so any
document format can be ingested. Simplified routing so text/plain
goes to text-load and everything else goes to document-load.
Removed dual inline/streaming data paths — documents always use
document_id for content retrieval.

New provenance entity types (tg:Section, tg:Image) and metadata
predicates (tg:elementTypes, tg:tableCount, tg:imageCount) for
richer explainability.

Universal decoder is in its own package (trustgraph-unstructured)
and container image (trustgraph-unstructured).

trustgraph-unstructured/pyproject.toml

@@ -0,0 +1,34 @@
+[build-system]
+requires = ["setuptools>=61.0", "wheel"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "trustgraph-unstructured"
+dynamic = ["version"]
+authors = [{name = "trustgraph.ai", email = "security@trustgraph.ai"}]
+description = "TrustGraph provides a means to run a pipeline of flexible AI processing components in a flexible means to achieve a processing pipeline."
+readme = "README.md"
+requires-python = ">=3.8"
+dependencies = [
+    "trustgraph-base>=2.2,<2.3",
+    "pulsar-client",
+    "prometheus-client",
+    "python-magic",
+    "unstructured[csv,docx,epub,md,odt,pptx,rst,rtf,tsv,xlsx]",
+]
+classifiers = [
+    "Programming Language :: Python :: 3",
+    "Operating System :: OS Independent",
+]
+
+[project.urls]
+Homepage = "https://github.com/trustgraph-ai/trustgraph"
+
+[project.scripts]
+universal-decoder = "trustgraph.decoding.universal:run"
+
+[tool.setuptools.packages.find]
+include = ["trustgraph*"]
+
+[tool.setuptools.dynamic]
+version = {attr = "trustgraph.unstructured_version.__version__"}