fix(repairs): Log repair submit silently ignored with empty defaults

The broken-model UUID fields used z.string().uuid().optional(), which
only accepts undefined — not the '' defaults. When the broken serial
matched an existing part, those fields unmounted before their
FormMessage could render, so handleSubmit aborted on hidden errors and
the mutation never fired. Accept the empty-string sentinel alongside
UUIDs.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

apps/web/src/components/repairs/LogRepairDialog.tsx

@@ -44,9 +44,9 @@ const Schema = z
   .object({
     hostId: z.string().uuid('Pick a host'),
     brokenSerial: z.string().trim().min(1, 'Required').max(128),
-    brokenPartModelId: z.string().uuid().optional(),
+    brokenPartModelId: z.union([z.literal(''), z.string().uuid()]).optional(),
     brokenMpn: z.string().trim().max(128).optional(),
-    brokenManufacturerId: z.string().uuid().optional(),
+    brokenManufacturerId: z.union([z.literal(''), z.string().uuid()]).optional(),
     replacementSerial: z.string().trim().min(1, 'Required').max(128),
     fmId: z.string().optional(),
     brokenExists: z.boolean().optional(),