Issue #3612599: Rename yoyaku_seating to yoyaku_placement and seat to place

Phase 2 of the placement generalization (parent #3612598). A behavior-preserving rename of the yoyaku_seating submodule to yoyaku_placement, and of its assignable unit from a seat to a generic place (a seat, box, table, booth or desk).

Renamed

• Module yoyaku_seating to yoyaku_placement (plus _io and _example)
• Entity yoyaku_seat to yoyaku_place (keeps row and position, so adjacent-place selection still works), yoyaku_seat_grade to yoyaku_grade, yoyaku_seat_configuration to yoyaku_configuration
• Classes, services, routes, JS and CSS assets, the booking place field and the documentation all follow
• French translation realigned to the new source strings

Not changed

No feature was removed or altered. Adjacency, the venue map, grades, configurations and the one-place-per-slot constraint all behave exactly as before.

Verification

• 28 kernel tests pass (536 assertions)
• phpcs (Drupal + DrupalPractice, warnings enabled), phpstan and cspell all clean on the module
• No residual seat tokens remain across the module