Add parameterized SQL queries with nginx variables

New Feature: sqlite_param Directive
- Allows passing nginx variables as SQL prepared statement parameters
- Supports query parameters ($arg_name), path captures ($1, $2), headers, etc.
- Safe SQL injection protection via rusqlite prepared statements
- Multiple parameters supported (bound in order to ? placeholders)

Implementation:
- New sqlite_param directive for adding query parameters
- Variable resolution using ngx_http_get_variable() FFI
- UTF-8 validation on all variable values
- Updated execute_query() to accept parameter array
- rusqlite::ToSql parameter binding

Examples:
- Book detail by ID: /book?id=1
- Genre filtering: /genre?genre=Programming
- Year range search: /years?min=2015&max=2024

New Files:
- conf/book_detail.conf: Parameter examples configuration
- server_root/book/detail.hbs: Book detail page template
- server_root/genre/genre.hbs: Genre filter page template
- start_book_detail.sh: Quick start script for params example
- README.md: Comprehensive project documentation
- README_PARAMETERS.md: Parameters feature documentation

Configuration:
- MainConfig now supports global_templates_dir
- ModuleConfig extended with query_params Vec
- Handler resolves variables at request time
- Template paths adjusted for exact location matches

All examples tested and working with both static and parameterized queries.

start_book_detail.sh

@@ -0,0 +1,39 @@
+#!/usr/bin/env bash
+# Start script for the book detail example with path parameters
+
+set -e
+
+echo "📚 Starting Book Detail Example with Path Parameters..."
+echo ""
+
+# Check if database exists
+if [ ! -f "book_catalog.db" ]; then
+    echo "Database not found. Running setup..."
+    ./setup_book_catalog.sh
+    echo ""
+fi
+
+# Check if module is built
+if [ ! -f "target/debug/libnginx_test.dylib" ]; then
+    echo "Module not built. Building..."
+    direnv exec "$PWD" cargo build
+    echo ""
+fi
+
+# Start nginx
+echo "Starting nginx on http://localhost:8081"
+./ngx_src/nginx-1.28.0/objs/nginx -c conf/book_detail.conf -p .
+
+echo ""
+echo "✅ Book Detail Example is running!"
+echo ""
+echo "Try these URLs:"
+echo "  • http://localhost:8081/book?id=1           - View book #1"
+echo "  • http://localhost:8081/book?id=5           - View book #5"
+echo "  • http://localhost:8081/genre?genre=Programming   - Programming books"
+echo "  • http://localhost:8081/genre?genre=Databases     - Database books"
+echo "  • http://localhost:8081/years?min=2000&max=2010   - Books from 2000-2010"
+echo "  • http://localhost:8081/years?min=2015&max=2024   - Books from 2015-2024"
+echo ""
+echo "To stop: ./ngx_src/nginx-1.28.0/objs/nginx -s stop -c conf/book_detail.conf -p ."
+