fix frontend board mapping, game-over handling, and WASM-4

- fix Xform yx and add a shared view-aware board_position helper
- add GTK automatic game-over, restart, status, and multi-capture selection
- pin librsvg to the 2.60 series to match GTK4/glib 0.20
- add WASM orientation, undo/redo/new/flip controls, and winner overlay
- replace WASM crown images with canvas paths and remove dead files/deps
- make WASM-4 playable with mouse input, crowns, winner handling, and correct mapping
- move the WASM-4 release profile to the workspace root
- clean up frontend dead code and update the README

README.md

@@ -9,12 +9,16 @@ several front ends.
 | --- | --- |
 | `rdraught` | `no_std` game engine, move generation, AI, and undo/redo history. |
 | `rdraught-ui-common` | Small geometry and shared-state helpers used by the graphical front ends. |
-| `rdraught-gtk` | GTK4 desktop front end (the most complete one). |
-| `rdraught-wasm` | Browser front end using the Canvas 2D API and `wasm-bindgen`. |
-| `rdraught-w4` | WASM-4 front end. Work in progress. |
-| `rdraught-sdl` | SDL3 front end. Work in progress. |
+| `rdraught-gtk` | Playable GTK4 desktop front end. |
+| `rdraught-wasm` | Playable browser front end using the Canvas 2D API and `wasm-bindgen`. |
+| `rdraught-w4` | Playable WASM-4 front end. |
+| `rdraught-sdl` | SDL3 prototype; not wired to the game yet. |
 | `rdraught-cli` | Scratch `rustyline` program; not a playable CLI yet. |
 
+The GTK, WASM, and WASM-4 front ends are currently hot-seat games: both sides
+are played by people. The core AI is available but is not wired into a frontend
+yet.
+
 ## Rules
 
 The rules implemented by the engine are an 8x8 draughts variant:
@@ -35,7 +39,8 @@ The engine exposes a fixed-depth negamax search with alpha-beta pruning through
 `DraughtsGame::get_best_move(max_depth)`. A depth of zero is treated as one ply.
 Wins and losses dominate material scoring, and faster wins are preferred. The
 search has no time or node budget and no draw/repetition detection, so choose a
-modest depth for positions with many pieces.
+modest depth for positions with many pieces. The current frontends do not use
+the AI; they are hot-seat games.
 
 ## Requirements
 
@@ -79,6 +84,11 @@ below instead.
 cargo run -p rdraught-gtk
 ```
 
+Use the board orientation selector at startup, click a piece to select it, and
+click a highlighted destination to move. The header bar has undo, redo, and
+New Game buttons. The game-over dialog appears automatically; use New Game to
+start another game.
+
 ### Browser WASM
 
 ```sh
@@ -87,6 +97,13 @@ cd rdraught-wasm
 trunk serve --open
 ```
 
+Click a piece and then a highlighted destination. Keyboard controls:
+
+- `Ctrl+Z` — undo
+- `Ctrl+Y` or `Ctrl+Shift+Z` — redo
+- `N` — new game
+- `F` — flip the board orientation
+
 The `.cargo/config.toml` inside `rdraught-wasm` is only read when Cargo runs
 from that directory.
 
@@ -97,8 +114,12 @@ cd rdraught-w4
 cargo build --release --target wasm32-unknown-unknown
 ```
 
-Run Cargo from `rdraught-w4` so its linker configuration is applied. The
-resulting module is in `target/wasm32-unknown-unknown/release/`.
+Run Cargo from `rdraught-w4` so its linker configuration is applied. The module
+is written to `../target/wasm32-unknown-unknown/release/rdraught_w4.wasm`.
+
+Use the mouse to select a piece and click a highlighted destination to move.
+After a win, click to start a new game. The board is shown in a fixed
+orientation for hot-seat play.
 
 ### SDL3