refactor: rename all chunk flags to include explicit units

Replace ambiguous --chunk-size / --chunk-overlap names that meant different
things in different contexts (tokens vs characters) with fully explicit names:

- --chunk-size (RAG tokens)     → --chunk-tokens
- --chunk-overlap (RAG tokens)  → --chunk-overlap-tokens
- --chunk (enable RAG chunking) → --chunk-for-rag
- --streaming-chunk-size (chars) → --streaming-chunk-chars
- --streaming-overlap (chars)    → --streaming-overlap-chars
- --chunk-size (PDF pages)       → --pdf-pages-per-chunk (poc file)

Also aligns stream_parser.py help with streaming_ingest.py standalone parser.
All 2167 tests pass.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/skill_seekers/cli/doc_scraper.py

@@ -2227,8 +2227,8 @@ def execute_scraping_and_building(
         from skill_seekers.cli.rag_chunker import RAGChunker
 
         chunker = RAGChunker(
-            chunk_size=args.chunk_size,
-            chunk_overlap=args.chunk_overlap,
+            chunk_size=args.chunk_tokens,
+            chunk_overlap=args.chunk_overlap_tokens,
             preserve_code_blocks=not args.no_preserve_code_blocks,
             preserve_paragraphs=not args.no_preserve_paragraphs,
         )