docs(ui): define web application visual style requirements

MVP.md

@@ -215,7 +215,34 @@ Browser controls must support:
 - If the player does not reconnect within 60 seconds, the match ends in a draw.
 - Reloading a page is treated as a reconnect, not as leaving the match.
 
-## 11. Technical constraints
+## 11. Browser presentation
+
+- The browser UI uses one dark, humorous retro arcade visual language across
+  provisioning, lobby, player, and observer modes, as defined in
+  `docs/UI_STYLE.md`.
+- All player-facing UI copy, game messages, and browser errors are in Russian.
+- The UI uses a near-black background, purple panels, turquoise interactive
+  accents, blue for Player 1, pink for Player 2, and plant-like green maze
+  walls. Important state is distinguished by icons, labels, outlines, or
+  shapes in addition to color.
+- The player map consumes all space not required by fixed status and control
+  panels. The player view supports a minimum `412 x 916` CSS-pixel viewport
+  without page scrolling.
+- Computers support keyboard movement and on-screen arcade controls. Tablets
+  support swipes and on-screen controls. Phones use directional swipes without
+  on-screen directional buttons.
+- An always-visible `OK` control with a key icon drops the carried key without
+  confirmation and exposes the Russian accessible label `Сбросить ключ`.
+- Observer mode requires at least a `1024 x 768` CSS-pixel viewport, initially
+  fits the complete map, and supports zoom and pan. Smaller viewports show a
+  Russian large-screen requirement message.
+- Sound and vibration are enabled by default after the first user interaction
+  when the browser and device support them.
+- The application has no runtime internet dependency. It uses local assets,
+  locally authored SVG icons, plain CSS, and a system monospace font styled to
+  resemble a pixel font.
+
+## 12. Technical constraints
 
 - Target: ESP32-C6FH4, 4 MB Flash, no required PSRAM.
 - Build: PlatformIO, `espressif32@7.0.1`, ESP-IDF, compatible
@@ -224,6 +251,8 @@ Browser controls must support:
   MVP.
 - Static browser assets reside in LittleFS and should be compressed for the
   production image.
+- The complete compressed web payload must not exceed 1.5 MiB and must fit the
+  unchanged 1,984 KiB LittleFS partition.
 - HTTP serves the application and provisioning pages; WebSocket carries live
   lobby, control, and match messages.
 - The initial LwIP socket limit is 16.
@@ -232,7 +261,7 @@ Browser controls must support:
 - Active lobby and match state may live in RAM and need not survive an ESP
   reboot. Wi-Fi settings must survive reboot.
 
-## 12. MVP acceptance criteria
+## 13. MVP acceptance criteria
 
 The MVP is accepted when all of the following are demonstrated on the target
 board:
@@ -263,8 +292,12 @@ board:
     60-second reconnect timeout ends it as a draw.
 12. A representative match normally completes in approximately five minutes
     after balance tuning, without imposing a hard match timer.
+13. The Russian retro arcade UI follows `docs/UI_STYLE.md`, works at the
+    required player and observer viewport sizes in the current stable Chrome,
+    Safari, Firefox, and Edge releases, requires no runtime internet access,
+    and stays within the 1.5 MiB compressed web-asset budget.
 
-## 13. Explicitly outside MVP
+## 14. Explicitly outside MVP
 
 - More than two active players or more than one concurrent match.
 - More than four observers.
@@ -277,4 +310,3 @@ board:
 - Persistent match recovery after ESP reboot.
 - OTA firmware partitions and OTA update flow.
 - Dependence on PSRAM, an unverified LED, or an assumed board pinout.
-