/langs/tala and everything below it, which tala.run and earlier links
still point to, now redirect permanently to the language list of the
ViGet home page, like /langs, instead of answering 404. The README, the
architecture guide and the bug-report template name the C, C++ and
Objective-C catalogs.

A Google callback that could not finish ended in an unhandled 500: a
visitor who declined on Google's consent screen, a callback whose state
cookie had expired, and a direct request to the callback path all got an
empty error page. The account API document already promised a redirect
to /login?google=failed for a failed callback; the handler of the Google
scheme now does that through OnRemoteFailure. Three new tests cover a
callback without state, a declined consent and a forged state.

Three statements no longer matched the sites:

- the bug report template still named the catalog paths without the
  language and the build system; they are /langs/tala/<Publisher>/<Name>/
  and /dslplugins/tazel/<Publisher>/<Name>/;
- the operations guide placed Tala content on xsharp-lang.xyz, which only
  redirects to tala.run now;
- the architecture guide described the ViGet routing before the catalogs
  per language and build system: it now gives the rewrites of /langs/tala
  and /dslplugins/tazel, the redirects of /langs and /dslplugins, three
  indexed ViGet pages and a sitemap with the home page and both catalogs.

The language Visual X# is now Tala. The Progmasoft home page, the ViGet
pages, the dashboard and the two footers name it so in the four languages of
the site; the project file is BUILD.kts, and the source link leads to
Progmasoft/tala. The README, the operations and localization documents and
the issue templates follow.

The localization document said that a left-to-right mark follows the name of
the language in Hebrew text. That was for the `#` of the old name; the
sentence now speaks of names that end in a symbol.

The links to xsharp-lang.xyz stay: the language site is still served there.