Rename the venue drawing to the venue map, since it is geometry and not a picture

Renames the venue drawing to the venue map. The document carries the sprite ids, the grades, the sections and every place with its coordinates: it is the hall's geometry, and the picture is a separate file that already has its own name and its own URL.

• VenueMapBuilder: drawingDocument() to mapDocument(), drawingUrl() to mapDocumentUrl(), drawingCacheTags() to mapCacheTags(). The cache id fragment changes, so VERSION is bumped and the old entries retire rather than being read back under a name that no longer describes them.
• The payload keys the page hands the browser: mapUrl to mapDocumentUrl, backgroundUrl to artworkUrl. Put a URL in the address bar and the name should tell the truth; mapUrl returned JSON.
• Prose, test names and the French translation follow.

Two deviations from the issue, both flagged rather than hidden:

1. The issue proposed mapUrl() for the builder method. It is mapDocumentUrl(), because the issue's own test (does the name promise a page to browse?) applies to a URL wherever it lives, and it pairs with mapDocument().
2. Two drive-by fixes in files this touched anyway: mergePayload()'s docblock still documented a state parameter the fold replaced with availability, own and settings; and fr.po held an orphan msgid with the old wording of a field description, leaving the current one untranslated. Both are corrected.

What deliberately does not move: the route, the library, the ysm- class prefix, VenueMapBuilder, VenueMapController, VenueBackgroundUrl and the map_background field. Where the word means the act of drawing, or the architect's actual drawing in docs/venue-map.md, it stays.

Local runs: seven kernel classes on MySQL, plus VenueMapFetchTest (4/27) and VenueMapEndpointTest (10/87) against a served docroot, so the renamed keys are proven wired end to end. phpcs clean under the CI ruleset, phpstan level 1 unchanged, eslint and stylelint clean.