fix: preserve + and . in wiki slugs, clean stray plus signs

Allow C++, .NET, version numbers (2.0.1) in wiki filenames.
Clean up isolated plus signs that appear between hyphens.

Examples:
- C++ vs C# -> C++-vs-C.md
- .NET Guide -> .NET-Guide.md
- version 2.0.1 -> version-2.0.1-release.md

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

services/wiki/wiki_path.go

@@ -150,16 +150,18 @@ func WebPathFromRequest(s string) WebPath {
 }
 
 var multiHyphenRe = regexp.MustCompile(`-{2,}`)
-var nonAlphanumRe = regexp.MustCompile(`[^a-zA-Z0-9\-]`)
+var nonSlugRe = regexp.MustCompile(`[^a-zA-Z0-9+.\-]`)
 
 // sanitizeWikiTitle converts a user-provided title into a clean, URL-friendly slug.
 // Spaces and special characters become hyphens, consecutive hyphens collapse to one.
+// Preserves: letters, digits, hyphens, plus signs (+), and dots (.)
 func sanitizeWikiTitle(title string) string {
 	title = strings.TrimSpace(title)
 	title = strings.ReplaceAll(title, " ", "-")
-	title = nonAlphanumRe.ReplaceAllString(title, "-")
+	title = nonSlugRe.ReplaceAllString(title, "-")
 	title = multiHyphenRe.ReplaceAllString(title, "-")
-	title = strings.Trim(title, "-")
+	title = strings.NewReplacer("-+-", "-", "+-", "-", "-+", "-").Replace(title) // clean stray plus signs
+	title = strings.Trim(title, "-+.")
 	return title
 }