Nothing reads from the store now that the detail page uses GraphQL,
so SubmitSightingPage no longer adds sightings to it. The mock
sightings move to tests/ because the tests still use them as
fixtures.

Closes #35

Give the fake backend an optional latency so states that only exist
while waiting can be tested, and test the first load, a serach with
no matches and a new serach while old results are shown.

Refs #43

Clear the cached sighting lists after a submit so the new sighting
shows up in the search results. Show "Unknown" for a missing shape
and hide empty comments. Return "Unknown date" for invalid dates
instead of throwing. Return not found for ids that are not plain
numbers, since MySQL reads '1abc' as 1.

Part of #35

The detail page said "Check your connection" for every error. If
the backend answers with a GraphQL error, such as a database
failure, it now says the server could not load the sighting and
hides the retry button, since retrying won't help.

Network
failures keep the old message and the button.

Part of #35

…e-backen' into 43-update-component-tests-for-apollo

The summary counted keys in the errors object, but fixing a field
set its error to undefined without removing the key.
Now it checks for actual messages instead.

Fixes #63

Check that an invalid form sends no request and links each error to
its feild, that the error summary goes away once the fileds are fixed,
that a double click sends on requests, and that a sbmitted
sighting shows up in the search list. Uses a fake database
that stores the sighting and counts requests.

Refs #43, #64

npm test started Vitest in watch mode and only reached
the backend tests after quitting it. Run Vitest once by
default, like CI, and moved watch mode to npm run test:watch.
Documented in AGENTS.md.

Refs #43