refactor: rewrite duckduckgo-search skill for accuracy and usability

Follow-up to PR #267 merge:
- Fix CLI syntax: -k is keywords, -m is max results (was reversed)
- Add clear trigger condition: use only when web_search tool unavailable
- Remove misleading curl fallback (DuckDuckGo Instant Answer API is not
  a web search endpoint)
- Fix package name: ddgs (renamed from duckduckgo-search)
- Add workflow section for search → web_extract pipeline
- Add pitfalls and limitations sections
- Fix author attribution to actual contributor
- Rewrite shell script as simple ddgs wrapper with availability check

skills/research/duckduckgo-search/scripts/duckduckgo.sh

@@ -1,32 +1,28 @@
 #!/bin/bash
 # DuckDuckGo Search Helper Script
-# Fallback for when ddgs library is unavailable
-# Usage: ./duckduckgo.sh [text|images|news|videos] <query> [limit]
+# Wrapper around ddgs CLI with sensible defaults
+# Usage: ./duckduckgo.sh <query> [max_results]
 
 set -e
 
-MODE="${1:-text}"
-QUERY="$2"
-LIMIT="${3:-5}"
+QUERY="$1"
+MAX_RESULTS="${2:-5}"
 
 if [ -z "$QUERY" ]; then
-    echo "Usage: $0 [text|images|news|videos] <query> [limit]"
+    echo "Usage: $0 <query> [max_results]"
+    echo ""
     echo "Examples:"
-    echo "  $0 text 'python async' 5"
-    echo "  $0 images 'cat' 10"
+    echo "  $0 'python async programming' 5"
+    echo "  $0 'latest AI news' 10"
+    echo ""
+    echo "Requires: pip install ddgs"
     exit 1
 fi
 
-# URL encode query
-ENCODED_QUERY=$(echo "$QUERY" | sed 's/ /+/g' | sed 's/&/%26/g' | sed 's/=/%3D/g')
+# Check if ddgs is available
+if ! command -v ddgs &> /dev/null; then
+    echo "Error: ddgs not found. Install with: pip install ddgs"
+    exit 1
+fi
 
-case "$MODE" in
-    text|images|news|videos)
-        curl -s "https://api.duckduckgo.com/?q=${ENCODED_QUERY}&format=json&limit=${LIMIT}"
-        ;;
-    *)
-        echo "Unknown mode: $MODE"
-        echo "Valid modes: text, images, news, videos"
-        exit 1
-        ;;
-esac
+ddgs text -k "$QUERY" -m "$MAX_RESULTS"