refactor: rename diigo-dump to diigo-cache

Pure rename ahead of the dump worker's evolution into a bookmark cache
(goal 1c), so history follows the files. The diigo-login helper script
is dropped: the cookie now enters through webapp's mint form, never a
local script.

diigo-cache/wrangler.jsonc

@@ -0,0 +1,14 @@
+{
+	"$schema": "node_modules/wrangler/config-schema.json",
+	"name": "diigo-dump",
+	"main": "src/index.ts",
+	"compatibility_date": "2026-09-29",
+	"observability": { "enabled": true },
+	"services": [
+		{
+			"binding": "WEBAPP",
+			"service": "webapp",
+			"entrypoint": "WebAppFactory"
+		}
+	]
+}