Add scripts/stage-plugins.sh and run-sample.sh for running the engine locally

Contracts and Implementation build into two separate bin/ folders, so
there's nowhere valid to point --plugins at without a staging step first
— every manual verification this session has done that staging by hand.
stage-plugins.sh does it for every plugin in one pass; run-sample.sh
stages then runs samples/WindowDemo windowed, forwarding extra args to
`engine run` (e.g. --screenshot).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01N1qPfzq8TDCUMFMV3UwV5N

scripts/run-sample.sh

@@ -0,0 +1,14 @@
+#!/usr/bin/env bash
+# Stages every plugin, then runs samples/WindowDemo windowed. Extra args
+# are forwarded to `engine run` — e.g. ./run-sample.sh --screenshot out.png
+set -euo pipefail
+
+REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+CONFIG="${CONFIGURATION:-Debug}"
+STAGE_DIR="$REPO_ROOT/.stage/plugins"
+
+"$REPO_ROOT/scripts/stage-plugins.sh" "$STAGE_DIR"
+
+cd "$REPO_ROOT/samples/WindowDemo"
+exec dotnet "$REPO_ROOT/src/Engine.Host/bin/$CONFIG/net9.0/Engine.Host.dll" run --windowed \
+    --plugins "$STAGE_DIR" --project project.json --scene scene.json "$@"

scripts/stage-plugins.sh

@@ -0,0 +1,37 @@
+#!/usr/bin/env bash
+# Builds every plugin and lays each one out into a single flat directory
+# per id — plugin.json alongside its built DLLs — which is the layout
+# PluginHost.Load actually expects. Needed because Contracts and
+# Implementation build into two separate bin/ folders; without this step
+# there's nowhere valid to point --plugins at.
+set -euo pipefail
+
+REPO_ROOT="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+STAGE_DIR="${1:-$REPO_ROOT/.stage/plugins}"
+CONFIG="${CONFIGURATION:-Debug}"
+
+echo "Building solution ($CONFIG)..."
+dotnet build "$REPO_ROOT/LinguaEngine.sln" -c "$CONFIG" >/dev/null
+
+rm -rf "$STAGE_DIR"
+mkdir -p "$STAGE_DIR"
+
+for plugin_dir in "$REPO_ROOT"/plugins/*/; do
+    id="$(basename "$plugin_dir")"
+    [ -f "$plugin_dir/plugin.json" ] || continue
+
+    # engine.foo -> Engine.Foo (the Implementation project's folder name)
+    impl_name="$(awk -F. '{for(i=1;i<=NF;i++){$i=toupper(substr($i,1,1)) substr($i,2)}}1' OFS=. <<<"$id")"
+    impl_out="$plugin_dir/$impl_name/bin/$CONFIG/net9.0"
+
+    if [ ! -d "$impl_out" ]; then
+        echo "warning: no build output for '$id' at $impl_out, skipping" >&2
+        continue
+    fi
+
+    mkdir -p "$STAGE_DIR/$id"
+    cp -r "$impl_out/." "$STAGE_DIR/$id/"
+    cp "$plugin_dir/plugin.json" "$STAGE_DIR/$id/"
+done
+
+echo "Staged plugins into: $STAGE_DIR"