build(cloudflare): add a Cloudflare preview build target

DEPLOY_TARGET now selects the adapter; Netlify stays the default and NODE_ADAPTER
keeps working. Cloudflare compresses in transit, so the Worker build aliases
$lib/server/compression to a pass-through that leaves the streaming body alone.

CI builds and dry-run deploys this target. That is compilation and packaging
coverage only, not a production compatibility gate: native sharp still blocks the
share-preview route in the Worker runtime.

wrangler.jsonc

@@ -0,0 +1,13 @@
+{
+	"$schema": "node_modules/wrangler/config-schema.json",
+	"name": "livingdextracker-preview",
+	"main": ".svelte-kit/cloudflare/_worker.js",
+	"compatibility_date": "2026-09-15",
+	"compatibility_flags": ["nodejs_compat"],
+	"assets": {
+		"directory": ".svelte-kit/cloudflare",
+		"binding": "ASSETS"
+	},
+	"observability": { "enabled": true },
+	"vars": { "POKEDEX_PERFORMANCE": "true" }
+}