docs: add --mode deep to graphify extract CLI reference

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

README.md

@@ -489,6 +489,7 @@ graphify extract ./docs --token-budget 30000   # smaller semantic chunks for loc
 graphify extract ./docs --max-concurrency 2    # fewer parallel LLM calls (useful for local inference)
 graphify extract ./docs --api-timeout 900      # longer HTTP timeout for slow local models (default 600s)
 graphify extract ./docs --google-workspace     # export .gdoc/.gsheet/.gslides via gws before extraction
+graphify extract ./docs --mode deep            # richer semantic extraction via extended system prompt
 graphify extract ./docs --no-cluster           # raw extraction only, skip clustering
 graphify extract ./docs --force                # overwrite graph.json even if new graph has fewer nodes (use after refactors or to clear ghost duplicates)
 graphify extract ./docs --dedup-llm            # LLM tiebreaker for ambiguous entity pairs (uses same API key)