Free drag & drop with fixed positions, empty cells and kept pages (0.2.31)

Tiles get an absolute grid slot instead of a packed order: a tile lands exactly
where it is dropped, dropping on another tile swaps the two, everything else
stays put, and empty cells and empty pages persist. The mockup previews the
result while dragging, a new page waits below the last one, "Pagina toevoegen"
keeps an empty page, empty cells accept the next tile from the picker, and the
mouse no longer selects text while dragging.

Storage and protocol stay version 1: `tiles[].slot` (0-47) and `pages` (1-8)
are additive, the layout message carries `slots` and `pages`. Firmware 0.2.26
places tiles on those slots (`place()` next to `pack()`); older firmware packs
in order as before and the editor says so.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

screen_manager/app/server.py

@@ -14,7 +14,7 @@ import tile_icons
 from updates import Updater
 
 from aiohttp import ClientSession, ClientTimeout, WSMsgType, web
-from core import BUILTIN, TILE_BACKGROUNDS, controls_catalogue, discover, extras, min_firmware, packets, state_message, validate_layout, validate_settings
+from core import BUILTIN, TILE_BACKGROUNDS, controls_catalogue, discover, extras, min_firmware, pack_slots, packets, state_message, validate_layout, validate_settings
 from zoneinfo import ZoneInfo
 
 LOG = logging.getLogger('screen_manager')
@@ -269,6 +269,12 @@ class Manager:
                     tile['options'][key]=old_options[key]
             if 'options' not in tile and 'options' in old_tiles.get(tile['entity'],{}):
                 tile['options'] = old_tiles[tile['entity']]['options'].copy()
+        # Restored options can widen a tile: an editor without positions packs again with
+        # the real widths, and explicit positions are checked once more for overlap.
+        if not any(isinstance(t, dict) and 'slot' in t for t in data.get('tiles', [])):
+            for tile, slot in zip(layout['tiles'], pack_slots(layout['tiles'])):
+                tile['slot'] = slot
+        layout = validate_layout(layout)
         known = {e['id'] for e in entities} | set(BUILTIN)
         if any(t['entity'] not in known for t in layout['tiles']):
             raise ValueError('Een gekozen entiteit bestaat niet meer. Zoek de nieuwe entiteit op.')
@@ -327,8 +333,12 @@ class Manager:
         if needed:
             self.status[inbox]=f"Indeling bewaard; firmware {needed}+ nodig voor deze tegels"
             return
-        messages = [{'v': 1, 'op': 'layout', 'inbox': inbox, 'title': layout['title'], 'entities': [t['entity'] for t in layout['tiles']],
-                     'keepalive': KEEPALIVE_SECONDS}]
+        tiles = layout['tiles']
+        # Grid positions (firmware 0.2.26+; older firmware ignores them and packs the entities in order).
+        messages = [{'v': 1, 'op': 'layout', 'inbox': inbox, 'title': layout['title'], 'entities': [t['entity'] for t in tiles],
+                     'slots': [t['slot'] for t in tiles], 'keepalive': KEEPALIVE_SECONDS}]
+        if 'pages' in layout:
+            messages[0]['pages'] = layout['pages']
         if 'settings' in layout:
             messages[0]['settings'] = {k:v for k,v in layout['settings'].items() if k not in ('swipe_pages','rotation')}
             messages[0]['swipe_pages'] = layout['settings'].get('swipe_pages',False)