feat(cli): Phase 2 - Organize RAG arguments into common.py (DRY principle)

Changes:
- Added RAG_ARGUMENTS dict to common.py with 3 flags:
  - --chunk-for-rag (enable semantic chunking)
  - --chunk-size (default: 512 tokens)
  - --chunk-overlap (default: 50 tokens)
- Removed duplicate RAG arguments from create.py and scrape.py
- Used .update() pattern to merge RAG_ARGUMENTS into UNIVERSAL_ARGUMENTS and SCRAPE_ARGUMENTS
- Added helper functions: add_rag_arguments(), get_rag_argument_names()
- Updated tests to reflect new argument count (15 → 13 universal arguments)
- Fixed test expectations for boolean_args (removed 'enhance', 'enhance_local')

Result:
- Single source of truth for RAG arguments in common.py
- DRY principle maintained across all commands
- All 88 key tests passing

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/skill_seekers/cli/arguments/create.py

@@ -13,6 +13,7 @@ import argparse
 from typing import Dict, Any, Set, List
 
 from skill_seekers.cli.constants import DEFAULT_RATE_LIMIT
+from .common import RAG_ARGUMENTS
 
 
 # =============================================================================
@@ -91,32 +92,8 @@ UNIVERSAL_ARGUMENTS: Dict[str, Dict[str, Any]] = {
             "help": "Minimize output (WARNING level only)",
         },
     },
-    # RAG features (NEW - universal for all sources!)
-    "chunk_for_rag": {
-        "flags": ("--chunk-for-rag",),
-        "kwargs": {
-            "action": "store_true",
-            "help": "Enable semantic chunking for RAG pipelines (all sources)",
-        },
-    },
-    "chunk_size": {
-        "flags": ("--chunk-size",),
-        "kwargs": {
-            "type": int,
-            "default": 512,
-            "metavar": "TOKENS",
-            "help": "Chunk size in tokens for RAG (default: 512)",
-        },
-    },
-    "chunk_overlap": {
-        "flags": ("--chunk-overlap",),
-        "kwargs": {
-            "type": int,
-            "default": 50,
-            "metavar": "TOKENS",
-            "help": "Overlap between chunks in tokens (default: 50)",
-        },
-    },
+    # RAG features (imported from common.py - see RAG_ARGUMENTS)
+    # Note: RAG arguments are merged into UNIVERSAL_ARGUMENTS at runtime
     # Preset system
     "preset": {
         "flags": ("--preset",),
@@ -138,6 +115,9 @@ UNIVERSAL_ARGUMENTS: Dict[str, Dict[str, Any]] = {
     },
 }
 
+# Merge RAG arguments from common.py into universal arguments
+UNIVERSAL_ARGUMENTS.update(RAG_ARGUMENTS)
+
 
 # =============================================================================
 # TIER 2: SOURCE-SPECIFIC ARGUMENTS