feat: implement comprehensive query paradigm zoo system (issue #62)

- Created extensible BaseQueryParadigm interface with standardized QueryResult format
- Implemented QueryParadigmRegistry for paradigm discovery and management
- Added 5 working paradigms: SQL, FTS, GraphQL, JSONPath, Natural Language
- Documented 9 additional paradigms: QBE, Batch Manipulation, Visual Query Builder, REST API, NoSQL, UNIX Pipeline, XPath/XQuery, RAG, Data Transformation
- Integrated full CLI interface: list, search, show, exec, categories commands
- Added comprehensive test suite with 23 test cases covering all components
- Auto-registration system enables easy addition of new paradigms
- Organized paradigms by category (structural, textual, semantic, visual, procedural, network) and complexity (beginner, intermediate, advanced)

🤖 Generated with [Claude Code](https://claude.ai/code)

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

markitect/query_paradigms/paradigms/xpath_paradigm.py

@@ -0,0 +1,115 @@
+"""
+XPath/XQuery Paradigm - Path-based data extraction.
+"""
+
+import time
+from typing import Dict, Any, List, Optional
+
+from ..base import BaseQueryParadigm, QueryResult
+
+
+class XPathParadigm(BaseQueryParadigm):
+    """XPath/XQuery paradigm for path-based data extraction."""
+
+    @property
+    def name(self) -> str:
+        return "XPath/XQuery"
+
+    @property
+    def description(self) -> str:
+        return "Path-based data extraction from structured documents using XPath and XQuery syntax"
+
+    @property
+    def category(self) -> str:
+        return "structural"
+
+    @property
+    def complexity(self) -> str:
+        return "advanced"
+
+    def execute(self, query: str, config: Dict[str, Any] = None) -> QueryResult:
+        """Execute XPath query (not yet implemented)."""
+        start_time = time.time()
+        execution_time = (time.time() - start_time) * 1000
+
+        return QueryResult(
+            paradigm=self.name,
+            query=query,
+            execution_time_ms=execution_time,
+            result_count=0,
+            results=[],
+            metadata={
+                "status": "not_implemented",
+                "implementation_issue": "TBD - to be created",
+                "description": "XPath enables precise navigation through document structures"
+            },
+            success=False,
+            error_message="XPath/XQuery paradigm not yet implemented."
+        )
+
+    def get_examples(self) -> List[Dict[str, str]]:
+        """Get example XPath queries."""
+        return [
+            {
+                "name": "Select files by attribute",
+                "description": "Find all files with specific author",
+                "query": "//file[@author='Alice']"
+            },
+            {
+                "name": "Deep path selection",
+                "description": "Select nested content elements",
+                "query": "//file/content/section[contains(@title, 'Introduction')]"
+            },
+            {
+                "name": "Conditional selection",
+                "description": "Select files with multiple conditions",
+                "query": "//file[@type='markdown' and @size > 1000]/tags/tag"
+            },
+            {
+                "name": "Position-based selection",
+                "description": "Select first 3 files by creation date",
+                "query": "//file[position() <= 3 and @created > '2024-01-01']"
+            }
+        ]
+
+    def validate_query(self, query: str) -> tuple[bool, Optional[str]]:
+        """Validate XPath query syntax."""
+        if not query.strip():
+            return False, "XPath query cannot be empty"
+
+        if not (query.startswith('//') or query.startswith('/')):
+            return False, "XPath query must start with / or //"
+
+        return True, None
+
+    def get_syntax_help(self) -> str:
+        """Get syntax help for XPath queries."""
+        return """XPath/XQuery Syntax:
+
+Basic Path Selection:
+//element - Select all elements anywhere
+/root/element - Select from root
+element[@attribute='value'] - Select by attribute
+
+Predicates:
+//file[@author='Alice'] - Attribute equals
+//file[position() <= 3] - Position-based
+//file[contains(@tags, 'tutorial')] - Text contains
+
+Functions:
+position() - Element position
+contains(string, substring) - Text contains
+count(elements) - Count elements
+text() - Get text content
+
+Document Structure (conceptual):
+//file - All files
+//file/@author - All author attributes
+//file/tags/tag - All tags in files
+//file[content/section] - Files with sections
+
+Examples:
+//file[@type='markdown']
+//file/tags/tag[text()='documentation']
+//file[@created > '2024-01-01' and @author='Alice']
+"""