Sight groups, DM reveal areas (cones), client-side image shrink for map upload

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01HJhXuLD2Z6hv3Wqeq9UL9K

README.md

@@ -142,6 +142,11 @@ The top of the lobby is one compact row: small buttons on the left (start fight,
 - **Fog of war:** with line of sight on, ground a player has already seen stays visible as a dimmed memory (**Fog** button; **↺** forgets it for everybody). The memory is a small mask per player and lobby, the dim picture is made on the server, so players never get pixels they have not seen.
 - **Sight range:** the map's value is the default (map editor); the number next to the Sight button changes it live for the lobby (reset when you switch maps).
 
+### Sight groups and revealing far away areas
+
+- **Sight groups** (Lobby actions, DM): players in the same group (A–D) share what they see; "Everyone shares sight" / "Everyone alone" are shortcuts. Tokens and ground seen by one member are visible to the whole group.
+- **👁 Reveal** (DM, line of sight on): click the spot the view starts from, then click where it ends (distance = range, direction = where it looks), pick the cone width and who sees it (everyone or chosen players), then **Reveal**. Walls block it like any other view. The area stays visible until you press **Hide**; afterwards it remains as dimmed memory (fog of war). Everything is computed on the server, so players only receive the pixels you showed them.
+
 ### Maps, tokens and line of sight
 
 - **Maps tab** (top navigation): all your maps with preview. Upload PNG, JPEG or WebP (up to 12 MB, 30 maps each; the server checks and re-encodes every image as WebP, max 4096 px per side, into `db/maps/`). **Edit** opens the map editor, **Share** gives other users access by username (like characters: they can put the map on their own table or **Copy** it, but not change it), **Duplicate** copies a map.