chore(webapp): drop the watch scenario kit

The seeder and its `scenarios:watch` script were only ever a way to reproduce a
watch condition by hand. The guidebook now states the conditions themselves, so
there is nothing left for the kit to be the answer to.

Author: kathiekiwi

apps/webapp/package.json

@@ -20,7 +20,6 @@
     "db:seed": "tsx seed.ts",
     "db:seed:ai-spans": "tsx seed-ai-spans.mts",
     "db:seed:queue-metrics": "tsx seed-queue-metrics.mts",
-    "scenarios:watch": "tsx seed-watch-scenarios.mts",
     "upload:sourcemaps": "bash ./upload-sourcemaps.sh",
     "test": "vitest --no-file-parallelism",
     "eval:dev": "evalite watch"