[ibrahimroshdy]

Closes #150, closes #151, closes #152.

Three map follow-ups to #137, one commit each. Ships in 1.10.6.

What a person can do

• Rooms open facing their screens (Map: open rooms facing the screens, not from behind #150). Open a room and the 3D view turns to the front of its monitor, TV or laptop, not their backs. Turn it another way inside the room and it opens that way next time on this device.
• Arms clamp at the back (Map: monitor arms clamp at the desk's back edge #151). Put on… or Add on it stands a monitor arm at the desk's back edge, the side away from the chair: centred, or at a back corner when the middle is taken. Its monitors hang over the desk in front of the pole. Turning the desk keeps it at the back; dragging it slides it along the back.
• Add on it reaches things not on the map (Map: Add on it lists things not on the map yet #152). A holder's Add on it also lists the room's things that aren't on the map yet, under Not on the map yet, with the shape each would get. Picking one puts it on the map and on the desk in one step: one Done, one Undo.

Try the map does all three (it shares the engine and the layout code).

How it works

• Facing: the turn most of the room's edge-mounted models have (weighted by width), seen from the diagonal with fewer walls in the way (rooms draw walls on two sides only). No screen: the view keeps its turn. A turn made in a room is stored per room in kept.map.turns (local storage, newest 200, failures ignored) and wins next time; the camera takes the short way round.
• Arms: freeSpot tries the back row first for an arm on a top (middle, nearest back corner, then anywhere along the back); dropOn snaps an arm to the back edge and turns it to the holder's way. Saved layouts load as saved.
• Add on it: offMapFor builds each off-map thing as the item it would become (thingItem, the D249 shape: chosen, saved, else the first suggestion) and keeps it only if that shape could be carried and fits the holder. addOn puts both kinds on in one plan change. The empty states no longer say "put one on the map first".
• Spec: one row, D237 (amendment, Map: open rooms facing the screens, not from behind #150–Map: Add on it lists things not on the map yet #152). Docs: a line each on the location map page. Four new strings, in all five catalogues.

Tested

• Web map suites: 7 files, 96 tests passed (new: facing.test.ts; arm back-edge cases in holders.test.ts, including a turned desk, the corner fallback and dragging; Add on it with off-map things, the one-step placement and the saved body in put-on.test.tsx).
• Try the map: sample.test.ts 6 passed; node scripts/check-try-kept.mjs: every walk passed; docs build OK.
• ci-local.sh --only lint,typecheck,drift OK; check-i18n every message in; check-logical-css OK.
• Screenshots (Try the map sample, desktop and phone, light): a turned office desk opening with the screen facing the view, a dual arm at the desk's back edge with two monitors, Add on it showing Not on the map yet.