The "user" input on `play.html` and on the other web pages
(`dashboard.html`, `jemalloc.html`, `merges.html`, `binary.html`,
`webterminal.html`) previously came pre-filled with the literal text
`default`. Replace that with an empty value and a `user` placeholder
hint. When the value is empty, the page does not send a `user=` query
parameter (or, in the WebTerminal protocol, omits the `user` field
from the auth JSON), letting the server fall back to its configured
default user — which is not necessarily named `default`.
For the WebTerminal, `parseAuthMessage` now treats the `user` field as
optional: when omitted or empty, the caller-provided default is
preserved. The call site seeds it with `default`, mirroring the HTTP
fallback in `authenticateUserByHTTP`.
Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>
