Major codebase cleanup after .insertr-add functionality overhaul

Consolidates duplicate code and removes technical debt accumulated during rapid development. This cleanup improves maintainability while preserving all functionality.

Backend cleanup:
- Remove unused legacy function findViableChildrenLegacy()
- Consolidate duplicate SQL null string helper functions into shared utils
- Unify text extraction functions across utils, engine, and id_generator
- Consolidate duplicate attribute getter functions into single implementation

Frontend cleanup:
- Remove duplicate authentication methods (authenticateWithOAuth vs performOAuthFlow)
- Remove unused hasPermission() method from auth.js
- Centralize repetitive API endpoint construction in api-client.js
- Reduce excessive console logging while preserving important error logs

Impact: -144 lines of code, improved maintainability, no functionality changes
All tests pass and builds succeed

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

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

internal/engine/utils.go

@@ -1,6 +1,7 @@
 package engine
 
 import (
+	"database/sql"
 	"strings"
 
 	"golang.org/x/net/html"
@@ -37,28 +38,6 @@ func getAttribute(node *html.Node, key string) string {
 	return ""
 }
 
-// extractTextContent gets the text content from an HTML node
-func extractTextContent(node *html.Node) string {
-	var text strings.Builder
-	extractTextRecursive(node, &text)
-	return strings.TrimSpace(text.String())
-}
-
-// extractTextRecursive recursively extracts text from node and children
-func extractTextRecursive(node *html.Node, text *strings.Builder) {
-	if node.Type == html.TextNode {
-		text.WriteString(node.Data)
-	}
-
-	for child := node.FirstChild; child != nil; child = child.NextSibling {
-		// Skip script and style elements
-		if child.Type == html.ElementNode &&
-			(child.Data == "script" || child.Data == "style") {
-			continue
-		}
-		extractTextRecursive(child, text)
-	}
-}
 
 // hasOnlyTextContent checks if a node contains only text content (no nested HTML elements)
 // DEPRECATED: Use hasEditableContent for more sophisticated detection
@@ -324,32 +303,6 @@ func hasInsertrClass(node *html.Node) bool {
 	return false
 }
 
-// findViableChildrenLegacy uses the old text-only logic for backwards compatibility
-func findViableChildrenLegacy(node *html.Node) []*html.Node {
-	var viable []*html.Node
-
-	for child := node.FirstChild; child != nil; child = child.NextSibling {
-		if child.Type == html.TextNode {
-			if strings.TrimSpace(child.Data) == "" {
-				continue
-			}
-		}
-
-		if child.Type != html.ElementNode {
-			continue
-		}
-
-		if isSelfClosing(child) {
-			continue
-		}
-
-		if hasOnlyTextContent(child) {
-			viable = append(viable, child)
-		}
-	}
-
-	return viable
-}
 
 // isSelfClosing checks if an element is typically self-closing
 func isSelfClosing(node *html.Node) bool {
@@ -389,7 +342,7 @@ func findElementWithContent(node *html.Node, targetTag, targetContent string) *h
 		classes := GetClasses(node)
 		if ContainsClass(classes, "insertr") {
 			// Content-based validation for precise matching
-			textContent := extractTextContent(node)
+			textContent := ExtractTextContent(node)
 			nodeContent := strings.TrimSpace(textContent)
 
 			if nodeContent == normalizedTarget {
@@ -422,3 +375,45 @@ func HasEditableContent(node *html.Node) bool {
 func FindViableChildren(node *html.Node) []*html.Node {
 	return findViableChildren(node)
 }
+
+// SQL utility functions for consistent null string handling
+
+// ToNullString converts a string to sql.NullString
+func ToNullString(s string) sql.NullString {
+	if s == "" {
+		return sql.NullString{Valid: false}
+	}
+	return sql.NullString{String: s, Valid: true}
+}
+
+// FromNullString converts sql.NullString to string
+func FromNullString(ns sql.NullString) string {
+	if ns.Valid {
+		return ns.String
+	}
+	return ""
+}
+
+// Text extraction utility functions
+
+// ExtractTextContent extracts all text content from an HTML node recursively
+func ExtractTextContent(node *html.Node) string {
+	var text strings.Builder
+	extractTextRecursiveUnified(node, &text)
+	return strings.TrimSpace(text.String())
+}
+
+// extractTextRecursiveUnified is the internal unified implementation
+func extractTextRecursiveUnified(node *html.Node, text *strings.Builder) {
+	if node.Type == html.TextNode {
+		text.WriteString(node.Data)
+	}
+	for child := node.FirstChild; child != nil; child = child.NextSibling {
+		// Skip script and style elements
+		if child.Type == html.ElementNode &&
+			(child.Data == "script" || child.Data == "style") {
+			continue
+		}
+		extractTextRecursiveUnified(child, text)
+	}
+}