fix: resolve 18 bugs and code quality issues across adaptors, CLI, and chunking pipeline

Bug fixes:
- Fix --var flag silently dropped in create routing (args.workflow_var → args.var)
- Fix double _score_code_quality() call in word scraper
- Add .docx file extension validation in WordToSkillConverter
- Fix weaviate ImportError masked by generic Exception handler
- Fix RAG chunking crash using non-existent converter.output_dir

Chunking pipeline improvements:
- Wire --chunk-overlap-tokens through entire package pipeline
  (package_skill → adaptor.package → format_skill_md → _maybe_chunk_content → RAGChunker)
- Add auto-scaling overlap: max(50, chunk_tokens//10) when chunk size is non-default
- Rename --no-preserve-code to --no-preserve-code-blocks (backward-compat alias kept)
- Replace hardcoded 512/50 chunk defaults with DEFAULT_CHUNK_TOKENS/DEFAULT_CHUNK_OVERLAP_TOKENS
  constants across all 12 concrete adaptors, rag_chunker, base, and package_skill

Code quality:
- Extract shared _generate_openai_embeddings() and _generate_st_embeddings() to SkillAdaptor
  base class, removing ~150 lines of duplication from chroma/weaviate/pinecone
- Add Pinecone adaptor with full upload support (pinecone_adaptor.py)

Tests (14 new):
- chunk_overlap_tokens parameter wiring, auto-scaling overlap, preserve_code_blocks flag
- .docx/.doc/no-extension file validation, --var flag routing E2E
- Embedding method inheritance verification, backward-compatible flag aliases

Docs:
- Update CHANGELOG, CLI_REFERENCE, API_REFERENCE, packaging guide (EN+ZH)
- Update README test count badge (1880+ → 2283+)

All 2283 tests passing, 8 skipped, 0 failures.

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

src/skill_seekers/cli/arguments/create.py

@@ -153,6 +153,15 @@ UNIVERSAL_ARGUMENTS: dict[str, dict[str, Any]] = {
             "metavar": "PATH",
         },
     },
+    "doc_version": {
+        "flags": ("--doc-version",),
+        "kwargs": {
+            "type": str,
+            "default": "",
+            "help": "Documentation version tag for RAG metadata (e.g., '16.2')",
+            "metavar": "VERSION",
+        },
+    },
 }
 
 # Merge RAG arguments from common.py into universal arguments
@@ -569,3 +578,11 @@ def add_create_arguments(parser: argparse.ArgumentParser, mode: str = "default")
     if mode in ["advanced", "all"]:
         for arg_name, arg_def in ADVANCED_ARGUMENTS.items():
             parser.add_argument(*arg_def["flags"], **arg_def["kwargs"])
+
+    # Deprecated alias for backward compatibility (removed in v4.0.0)
+    parser.add_argument(
+        "--no-preserve-code",
+        dest="no_preserve_code_blocks",
+        action="store_true",
+        help=argparse.SUPPRESS,
+    )