This re-implements the auth store with pinia.

Other notable changes:
* the OIDC client configuration and setup is now part of
  separate module that can be included by the OIDC callback routes
  and ensures that we always use the same OIDC client configuration.
* Authorization headers for the steering and tank REST APIs are now
  set with an axios interceptor instead of specifying them for each
  API store action.

refs #127

The show selection mechanism relied on the parent component to notify
other components, even though the selected show is already part of the
store and all component state can and should be derived from there.

Users should always be able to add new shows even if none have been
created thus far.

refs #97

This is a stopgap measure until we’ve worked on #17 [1] and added a
management interface for simple models like funding categories and show
types.

refs #97

[1] #17

Up until now we had two different show selectors based on the number of
shows that were available. We now use the same show selector for any
number of shows.

Apart from that shows are now sorted
 1. based on their active state (descending, so inactive last) and
 2. their name (ascending, so A-Z)
in the show selector so it’s easier to find relevant shows.

Other changes:
* title handling has been moved into PageHeader component
* calendar management has been removed and is now handled
  locally in the EmissionManager component
* inactive shows are badged

refs #122

Tank only returns an entries property for playlist objects if the
entries list would have at least one item. This is a bug [1].

closes #119

[1] tank#46

Up until now the application was crammed in a single JavaScript file
once bundled. This forces clients to download 1.1MiB of JavaScript all
at once.

Vite uses dynamic import statements as split-points for bundles. By
using dynamic imports for our routes we can delay the loading of some
data to a later point in time when the user actually needs it. We should
still try to reduce our overall bundle size.

closes #125

data.start wasn’t always defined so that the generated url would
sometimes contain "start=undefined".

refs #88

* basepath normalization: String.replace is not in-place.
* params: unshift adds array items, we wanted to pop the last item.

It’s nice to be able to select a week in the calendar and share it by
simply copying the URL so that another person may view the same week in
their browser.

This was accidentally removed when migrating to fullcalendar v5 in
14a9ff20.

Accessing the $parent should only be used in rare cases. Login session
handling is already implemented as part of the store, so there is no
need to use the App component as handler.