Add custom slugs, restore UI, UTM builder, and CLI link tools

src/utils/validation.rs

@@ -0,0 +1,19 @@
+pub fn validate_custom_slug(slug: &str) -> bool {
+    if !slug.starts_with('!') {
+        return false;
+    }
+    let rest = &slug[1..];
+    if rest.is_empty() || rest.len() > 24 {
+        return false;
+    }
+    rest.chars()
+        .all(|c| c.is_ascii_lowercase() || c.is_ascii_digit() || c == '-' || c == '_')
+}
+
+pub fn validate_redirect_code(code: &str) -> bool {
+    (code.len() == 6 && code.chars().all(|c| c.is_ascii_hexdigit())) || validate_custom_slug(code)
+}
+
+pub fn validate_page_code(code: &str) -> bool {
+    (code.len() == 4 && code.chars().all(|c| c.is_ascii_hexdigit())) || validate_custom_slug(code)
+}