Workers no longer run `npm ci` — `node_modules` and framework binaries
are restored from actions/cache populated once by a new `prep-deps` job.
This closes the intermittent EEXIST/ENOENT failure inside npm's own
cacache writer that occasionally fails `npm ci` on a runner. Removing
`npm ci` from workers also cuts ~5 min of duplicated install work per worker.
dispatch-begin now runs as its own job after prep-deps so it fires once the
per-worker test-server setup is the only remaining work before dispatch-run.
* Update E2E test workflows to use context names and server images and bump playwright workers to 10
* refactor: update branch naming conventions in E2E test workflows for better aggregation
