feat(tui): overlay positioning API with CSS-like values

Add OverlayOptions for configurable positioning (anchor, margins, offsets,
percentages). Add OverlayHandle for programmatic visibility control with
hide/setHidden/isHidden. Add visible callback for responsive overlays.

Extension API: ctx.ui.custom() now accepts overlayOptions and onHandle callback.

Examples: overlay-qa-tests.ts (10 test commands), doom-overlay (DOOM at 35 FPS).

packages/coding-agent/examples/extensions/doom-overlay/doom/build.sh

@@ -0,0 +1,152 @@
+#!/bin/bash
+# Build DOOM for pi-doom using doomgeneric and Emscripten
+
+set -e
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+PROJECT_ROOT="$(dirname "$SCRIPT_DIR")"
+DOOM_DIR="$PROJECT_ROOT/doom"
+BUILD_DIR="$PROJECT_ROOT/doom/build"
+
+echo "=== pi-doom Build Script ==="
+
+# Check for emcc
+if ! command -v emcc &> /dev/null; then
+    echo "Error: Emscripten (emcc) not found!"
+    echo ""
+    echo "Install via Homebrew:"
+    echo "  brew install emscripten"
+    echo ""
+    echo "Or manually:"
+    echo "  git clone https://github.com/emscripten-core/emsdk.git ~/emsdk"
+    echo "  cd ~/emsdk && ./emsdk install latest && ./emsdk activate latest"
+    echo "  source ~/emsdk/emsdk_env.sh"
+    exit 1
+fi
+
+# Clone doomgeneric if not present
+if [ ! -d "$DOOM_DIR/doomgeneric" ]; then
+    echo "Cloning doomgeneric..."
+    cd "$DOOM_DIR"
+    git clone https://github.com/ozkl/doomgeneric.git
+fi
+
+# Create build directory
+mkdir -p "$BUILD_DIR"
+
+# Copy our platform file
+cp "$DOOM_DIR/doomgeneric_pi.c" "$DOOM_DIR/doomgeneric/doomgeneric/"
+
+echo "Compiling DOOM to WebAssembly..."
+cd "$DOOM_DIR/doomgeneric/doomgeneric"
+
+# Resolution - 640x400 is doomgeneric default, good balance of speed/quality
+RESX=${DOOM_RESX:-640}
+RESY=${DOOM_RESY:-400}
+
+echo "Resolution: ${RESX}x${RESY}"
+
+# Compile with Emscripten (no sound)
+emcc -O2 \
+    -s WASM=1 \
+    -s EXPORTED_FUNCTIONS="['_doomgeneric_Create','_doomgeneric_Tick','_DG_GetFrameBuffer','_DG_GetScreenWidth','_DG_GetScreenHeight','_DG_PushKeyEvent','_malloc','_free']" \
+    -s EXPORTED_RUNTIME_METHODS="['ccall','cwrap','getValue','setValue','FS']" \
+    -s ALLOW_MEMORY_GROWTH=1 \
+    -s INITIAL_MEMORY=33554432 \
+    -s MODULARIZE=1 \
+    -s EXPORT_NAME="createDoomModule" \
+    -s ENVIRONMENT='node' \
+    -s FILESYSTEM=1 \
+    -s FORCE_FILESYSTEM=1 \
+    -s EXIT_RUNTIME=0 \
+    -s NO_EXIT_RUNTIME=1 \
+    -DDOOMGENERIC_RESX=$RESX \
+    -DDOOMGENERIC_RESY=$RESY \
+    -I. \
+    am_map.c \
+    d_event.c \
+    d_items.c \
+    d_iwad.c \
+    d_loop.c \
+    d_main.c \
+    d_mode.c \
+    d_net.c \
+    doomdef.c \
+    doomgeneric.c \
+    doomgeneric_pi.c \
+    doomstat.c \
+    dstrings.c \
+    f_finale.c \
+    f_wipe.c \
+    g_game.c \
+    hu_lib.c \
+    hu_stuff.c \
+    i_cdmus.c \
+    i_input.c \
+    i_endoom.c \
+    i_joystick.c \
+    i_scale.c \
+    i_sound.c \
+    i_system.c \
+    i_timer.c \
+    i_video.c \
+    icon.c \
+    info.c \
+    m_argv.c \
+    m_bbox.c \
+    m_cheat.c \
+    m_config.c \
+    m_controls.c \
+    m_fixed.c \
+    m_menu.c \
+    m_misc.c \
+    m_random.c \
+    memio.c \
+    p_ceilng.c \
+    p_doors.c \
+    p_enemy.c \
+    p_floor.c \
+    p_inter.c \
+    p_lights.c \
+    p_map.c \
+    p_maputl.c \
+    p_mobj.c \
+    p_plats.c \
+    p_pspr.c \
+    p_saveg.c \
+    p_setup.c \
+    p_sight.c \
+    p_spec.c \
+    p_switch.c \
+    p_telept.c \
+    p_tick.c \
+    p_user.c \
+    r_bsp.c \
+    r_data.c \
+    r_draw.c \
+    r_main.c \
+    r_plane.c \
+    r_segs.c \
+    r_sky.c \
+    r_things.c \
+    s_sound.c \
+    sha1.c \
+    sounds.c \
+    st_lib.c \
+    st_stuff.c \
+    statdump.c \
+    tables.c \
+    v_video.c \
+    w_checksum.c \
+    w_file.c \
+    w_file_stdc.c \
+    w_main.c \
+    w_wad.c \
+    wi_stuff.c \
+    z_zone.c \
+    dummy.c \
+    -o "$BUILD_DIR/doom.js"
+
+echo ""
+echo "Build complete!"
+echo "Output: $BUILD_DIR/doom.js and $BUILD_DIR/doom.wasm"