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/content/discoverer.go

@@ -393,9 +393,7 @@ func (disc *Discoverer) hasNoMeaningfulContent(node *html.Node) bool {
 	}
 
 	// Extract text content
-	var text strings.Builder
-	disc.extractTextRecursive(node, &text)
-	content := strings.TrimSpace(text.String())
+	content := engine.ExtractTextContent(node)
 
 	// Empty or whitespace-only content
 	if content == "" {
@@ -424,25 +422,6 @@ func (disc *Discoverer) hasNoMeaningfulContent(node *html.Node) bool {
 	return false
 }
 
-// extractTextRecursive extracts text content from a node and its children
-func (disc *Discoverer) extractTextRecursive(node *html.Node, text *strings.Builder) {
-	if node.Type == html.TextNode {
-		text.WriteString(node.Data)
-		return
-	}
-
-	for child := node.FirstChild; child != nil; child = child.NextSibling {
-		// Skip script and style content
-		if child.Type == html.ElementNode {
-			tag := strings.ToLower(child.Data)
-			if tag == "script" || tag == "style" {
-				continue
-			}
-		}
-		disc.extractTextRecursive(child, text)
-	}
-}
-
 // copyFile copies a file from input to output directory
 func (disc *Discoverer) copyFile(filePath, inputDir, outputDir string) error {
 	outputPath := disc.getOutputPath(filePath, inputDir, outputDir)