feat(utils): implement dual-field normalization for tags and contributors

Complete rewrite of normalization functions supporting dual-field architecture:

Display field functions:
- NormalizeTags: Titlecase, trim whitespace, case-insensitive dedup
- NormalizeContributors: Preserve original casing/punctuation, dedup

Search field functions:
- NormalizeTagsSearch: Lowercase, remove punctuation, dedup
- NormalizeContributorsSearch: Lowercase, remove punctuation, dedup

Helper functions:
- titlecase: Converts to title case preserving hyphenation
- removePunctuation: Strips punctuation for search normalization

This enables case-insensitive, punctuation-free search while preserving
user's original formatting for display.

internal/utils/tags.go

@@ -2,13 +2,37 @@ package utils
 
 import (
 	"strings"
+	"unicode"
+
+	"golang.org/x/text/cases"
+	"golang.org/x/text/language"
 )
 
-// NormalizeTags normalizes an array of tags by:
+// titleCaser is a global caser for titlecase conversion
-// 1. Converting to lowercase
+var titleCaser = cases.Title(language.Und, cases.NoLower)
-// 2. Trimming whitespace
+
-// 3. Removing duplicates
+// titlecase converts a string to title case while preserving hyphenation
-// 4. Removing empty strings
+// Example: "science fiction" → "Science Fiction", "non-fiction" → "Non-Fiction"
+func titlecase(s string) string {
+	return titleCaser.String(s)
+}
+
+// removePunctuation removes all punctuation characters from a string
+// Used for search field normalization only
+func removePunctuation(s string) string {
+	return strings.Map(func(r rune) rune {
+		if unicode.IsPunct(r) {
+			return -1
+		}
+		return r
+	}, s)
+}
+
+// NormalizeTags normalizes an array of tags for display:
+// 1. Trim whitespace
+// 2. Titlecase (preserves hyphenation)
+// 3. Case-insensitive deduplication
+// 4. Remove empty strings
 func NormalizeTags(tags []string) []string {
 	seen := make(map[string]struct{})
 	var normalized []string
@@ -22,10 +46,51 @@ func NormalizeTags(tags []string) []string {
 			continue
 		}
 
-		// Convert to lowercase
+		// Titlecase for display (preserves hyphenation: "Non-Fiction")
+		tag = titlecase(tag)
+
+		// Case-insensitive deduplication
+		key := strings.ToLower(tag)
+		if _, exists := seen[key]; !exists {
+			seen[key] = struct{}{}
+			normalized = append(normalized, tag)
+		}
+	}
+
+	return normalized
+}
+
+// NormalizeTagsSearch normalizes an array of tags for searching:
+// 1. Trim whitespace
+// 2. Remove punctuation
+// 3. Lowercase
+// 4. Case-insensitive deduplication
+// 5. Remove empty strings
+func NormalizeTagsSearch(tags []string) []string {
+	seen := make(map[string]struct{})
+	var normalized []string
+
+	for _, tag := range tags {
+		// Trim whitespace
+		tag = strings.TrimSpace(tag)
+
+		// Skip empty tags
+		if tag == "" {
+			continue
+		}
+
+		// Remove punctuation for search
+		tag = removePunctuation(tag)
+
+		// Lowercase for search
 		tag = strings.ToLower(tag)
 
-		// Check for duplicates
+		// Skip empty after removal
+		if tag == "" {
+			continue
+		}
+
+		// Case-insensitive deduplication
 		if _, exists := seen[tag]; !exists {
 			seen[tag] = struct{}{}
 			normalized = append(normalized, tag)
@@ -35,13 +100,85 @@ func NormalizeTags(tags []string) []string {
 	return normalized
 }
 
+// NormalizeContributors normalizes an array of contributors for display:
+// 1. Trim whitespace
+// 2. Preserve original casing (including CAPSLOCK companies)
+// 3. Preserve original punctuation for display
+// 4. Case-insensitive deduplication (removes punctuation for comparison only)
+// 5. Remove empty strings
+func NormalizeContributors(contributors []string) []string {
+	seen := make(map[string]struct{})
+	var normalized []string
+
+	for _, contributor := range contributors {
+		// Trim whitespace
+		contributor = strings.TrimSpace(contributor)
+
+		// Skip empty contributors
+		if contributor == "" {
+			continue
+		}
+
+		// Case-insensitive deduplication (remove punctuation for dedup check only)
+		dedupKey := removePunctuation(strings.ToLower(contributor))
+
+		// Keep original case and punctuation for display
+		if _, exists := seen[dedupKey]; !exists {
+			_seen[dedupKey] = struct{}{}
+			normalized = append(normalized, contributor)
+		}
+	}
+
+	return normalized
+}
+
+// NormalizeContributorsSearch normalizes an array of contributors for searching:
+// 1. Trim whitespace
+// 2. Remove punctuation
+// 3. Lowercase
+// 4. Case-insensitive deduplication
+// 5. Remove empty strings
+func NormalizeContributorsSearch(contributors []string) []string {
+	seen := make(map[string]struct{})
+	var normalized []string
+
+	for _, contributor := range contributors {
+		// Trim whitespace
+		contributor = strings.TrimSpace(contributor)
+
+		// Skip empty contributors
+		if contributor == "" {
+			continue
+		}
+
+		// Remove punctuation for search
+		contributor = removePunctuation(contributor)
+
+		// Lowercase for search
+		contributor = strings.ToLower(contributor)
+
+		// Skip empty after removal
+		if contributor == "" {
+			continue
+		}
+
+		// Case-insensitive deduplication
+		if _, exists := seen[contributor]; !exists {
+			seen[contributor] = struct{}{}
+			normalized = append(normalized, contributor)
+		}
+	}
+
+	return normalized
+}
+
 // JoinTags converts a string array to a comma-separated string
 // Maintained for backward compatibility with external systems
 func JoinTags(tags []string) string {
 	return strings.Join(tags, ", ")
 }
 
-// SplitTags converts a comma-separated string to a normalized array
+// SplitTags converts a comma-separated string to a normalized display array
 func SplitTags(tags string) []string {
 	if tags == "" {
 		return []string{}