feat: integrate excalidraw MCP into bootstrap and runtime setup

- install.sh: run mosaic-ensure-excalidraw post-install (non-fatal)
- runtime-setup.ts: configure excalidraw MCP during wizard setup
- bin/mosaic-ensure-excalidraw: install deps + register MCP with Claude
- runtime/mcp/EXCALIDRAW.json: MCP server config template
- tools/excalidraw/: headless .excalidraw → SVG export server

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

bin/mosaic-ensure-excalidraw

@@ -0,0 +1,119 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+MOSAIC_HOME="${MOSAIC_HOME:-$HOME/.config/mosaic}"
+TOOLS_DIR="$MOSAIC_HOME/tools/excalidraw"
+MODE="apply"
+SCOPE="user"
+
+err() { echo "[mosaic-excalidraw] ERROR: $*" >&2; }
+log() { echo "[mosaic-excalidraw] $*"; }
+
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+    --check) MODE="check"; shift ;;
+    --scope)
+      if [[ $# -lt 2 ]]; then
+        err "--scope requires a value: user|local"
+        exit 2
+      fi
+      SCOPE="$2"
+      shift 2
+      ;;
+    *)
+      err "Unknown argument: $1"
+      exit 2
+      ;;
+  esac
+done
+
+require_binary() {
+  local name="$1"
+  if ! command -v "$name" >/dev/null 2>&1; then
+    err "Required binary missing: $name"
+    return 1
+  fi
+}
+
+check_software() {
+  require_binary node
+  require_binary npm
+}
+
+check_tool_dir() {
+  [[ -d "$TOOLS_DIR" ]] || { err "Tool dir not found: $TOOLS_DIR"; return 1; }
+  [[ -f "$TOOLS_DIR/package.json" ]] || { err "package.json not found in $TOOLS_DIR"; return 1; }
+  [[ -f "$TOOLS_DIR/launch.sh" ]] || { err "launch.sh not found in $TOOLS_DIR"; return 1; }
+}
+
+check_npm_deps() {
+  [[ -d "$TOOLS_DIR/node_modules/@modelcontextprotocol" ]] || return 1
+  [[ -d "$TOOLS_DIR/node_modules/@excalidraw" ]] || return 1
+  [[ -d "$TOOLS_DIR/node_modules/jsdom" ]] || return 1
+}
+
+install_npm_deps() {
+  if check_npm_deps; then
+    return 0
+  fi
+  log "Installing npm deps in $TOOLS_DIR..."
+  (cd "$TOOLS_DIR" && npm install --silent) || {
+    err "npm install failed in $TOOLS_DIR"
+    return 1
+  }
+}
+
+check_claude_config() {
+  python3 - <<'PY'
+import json
+from pathlib import Path
+
+p = Path.home() / ".claude.json"
+if not p.exists():
+    raise SystemExit(1)
+try:
+    data = json.loads(p.read_text(encoding="utf-8"))
+except Exception:
+    raise SystemExit(1)
+mcp = data.get("mcpServers")
+if not isinstance(mcp, dict):
+    raise SystemExit(1)
+entry = mcp.get("excalidraw")
+if not isinstance(entry, dict):
+    raise SystemExit(1)
+cmd = entry.get("command", "")
+if not cmd.endswith("launch.sh"):
+    raise SystemExit(1)
+PY
+}
+
+apply_claude_config() {
+  require_binary claude
+  local launch_sh="$TOOLS_DIR/launch.sh"
+  claude mcp add --scope user excalidraw -- "$launch_sh"
+}
+
+# ── Check mode ────────────────────────────────────────────────────────────────
+
+if [[ "$MODE" == "check" ]]; then
+  check_software
+  check_tool_dir
+  if ! check_npm_deps; then
+    err "npm deps not installed in $TOOLS_DIR (run without --check to install)"
+    exit 1
+  fi
+  if ! check_claude_config; then
+    err "excalidraw not registered in ~/.claude.json"
+    exit 1
+  fi
+  log "excalidraw MCP is configured and available"
+  exit 0
+fi
+
+# ── Apply mode ────────────────────────────────────────────────────────────────
+
+check_software
+check_tool_dir
+install_npm_deps
+apply_claude_config
+log "excalidraw MCP configured (scope: $SCOPE)"