Fix: Remove UNIQUE constraint from microchip field to allow NULL values

server/db/init.js

@@ -26,7 +26,7 @@ function initDatabase(dbPath) {
       sex TEXT NOT NULL CHECK(sex IN ('male', 'female')),
       birth_date DATE,
       color TEXT,
-      microchip TEXT UNIQUE,
+      microchip TEXT,
       photo_urls TEXT, -- JSON array of photo URLs
       notes TEXT,
       is_active INTEGER DEFAULT 1,
@@ -35,6 +35,13 @@ function initDatabase(dbPath) {
     )
   `);
 
+  // Create unique index for microchip that allows NULL values
+  db.exec(`
+    CREATE UNIQUE INDEX IF NOT EXISTS idx_dogs_microchip 
+    ON dogs(microchip) 
+    WHERE microchip IS NOT NULL
+  `);
+
   // Parents table - Relationship mapping
   db.exec(`
     CREATE TABLE IF NOT EXISTS parents (