fix(index-builder): set wrangler CWD to /tmp for Pages deploy

wrangler creates .wrangler/tmp relative to its working directory.
The container runs as non-root user acb with WORKDIR=/app (root-owned),
so mkdir /app/.wrangler/tmp fails with EACCES. Setting cmd.Dir=/tmp
gives wrangler a writable CWD while keeping the /data output path
(absolute) unchanged.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cmd/acb-index-builder/deploy.go

@@ -108,6 +108,7 @@ func deployToPages(cfg *Config) error {
 
 	cmd := exec.CommandContext(ctx, "wrangler", args...)
 	cmd.Env = env
+	cmd.Dir = "/tmp" // wrangler creates .wrangler/tmp relative to CWD; /app is root-owned
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr