fix(backfill): an anonymous run says so at the END, where it is read

[cubehouse]

Every documented example omitted the API key. The docs are the smaller half of the problem.

Without a key the command succeeds. It reads the 7 days anonymous access allows, writes 433 rows of Magic Kingdom instead of ~94,000, and exits 0:

$ themeparks-backfill "magic kingdom" --out .
no API key: reading the 7 days anonymous access allows.
...
  done: 433 rows -> 75ea578a-….ndjson
$ echo $?
0

The notice is printed before a run that takes minutes, so it scrolls away, and the last thing on screen is done: 433 rows. For a customer who has just paid for 400 days that is indistinguishable from success — there is a file, there is no error, and the number means nothing unless you already know what it should have been.

A keyless example is worse than a broken one, because a broken one gets reported.

Changed

• The notice is repeated at the end of the run, naming what a key would have bought. Now the last four lines read that was ANONYMOUS ACCESS: the last 7 days only.
• The README and the command's own --help epilog export THEMEPARKS_API_KEY before the example that needs it, and keep saying --list does not — finding a park before you have paid is the point of that flag.

Two mutations pinned: dropping the closing notice, and firing it when a key was given. Both killed. 334 tests.

Companion: ThemeParks_JavaScript for the same change, and web for the two docs pages.

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