Incremental / large document loading (#659)

Tech spec

BlobStore (trustgraph-flow/trustgraph/librarian/blob_store.py):
- get_stream() - yields document content in chunks for streaming retrieval
- create_multipart_upload() - initializes S3 multipart upload, returns
  upload_id
- upload_part() - uploads a single part, returns etag
- complete_multipart_upload() - finalizes upload with part etags
- abort_multipart_upload() - cancels and cleans up

Cassandra schema (trustgraph-flow/trustgraph/tables/library.py):
- New upload_session table with 24-hour TTL
- Index on user for listing sessions
- Prepared statements for all operations
- Methods: create_upload_session(), get_upload_session(),
  update_upload_session_chunk(), delete_upload_session(),
  list_upload_sessions()

- Schema extended with UploadSession, UploadProgress, and new
  request/response fields
- Librarian methods: begin_upload, upload_chunk, complete_upload,
  abort_upload, get_upload_status, list_uploads
- Service routing for all new operations
- Python SDK with transparent chunked upload:
  - add_document() auto-switches to chunked for files > 10MB
  - Progress callback support (on_progress)
  - get_pending_uploads(), get_upload_status(), abort_upload(),
    resume_upload()

- Document table: Added parent_id and document_type columns with index
- Document schema (knowledge/document.py): Added document_id field for
  streaming retrieval
- Librarian operations:
  - add-child-document for extracted PDF pages
  - list-children to get child documents
  - stream-document for chunked content retrieval
  - Cascade delete removes children when parent is deleted
  - list-documents filters children by default
- PDF decoder (decoding/pdf/pdf_decoder.py): Updated to stream large
  documents from librarian API to temp file
- Librarian service (librarian/service.py): Sends document_id instead of
  content for large PDFs (>2MB)
- Deprecated tools (load_pdf.py, load_text.py): Added deprecation
  warnings directing users to tg-add-library-document +
  tg-start-library-processing

Remove load_pdf and load_text utils

Move chunker/librarian comms to base class

Updating tests

trustgraph-cli/pyproject.toml

@@ -54,9 +54,7 @@ tg-invoke-prompt = "trustgraph.cli.invoke_prompt:main"
 tg-invoke-structured-query = "trustgraph.cli.invoke_structured_query:main"
 tg-load-doc-embeds = "trustgraph.cli.load_doc_embeds:main"
 tg-load-kg-core = "trustgraph.cli.load_kg_core:main"
-tg-load-pdf = "trustgraph.cli.load_pdf:main"
 tg-load-sample-documents = "trustgraph.cli.load_sample_documents:main"
-tg-load-text = "trustgraph.cli.load_text:main"
 tg-load-turtle = "trustgraph.cli.load_turtle:main"
 tg-load-knowledge = "trustgraph.cli.load_knowledge:main"
 tg-load-structured-data = "trustgraph.cli.load_structured_data:main"