chore(deps): bump node from 22-slim to 26-slim in /docker

Bumps node from 22-slim to 26-slim.

---
updated-dependencies:
- dependency-name: node
  dependency-version: 26-slim
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

docker/Dockerfile

@@ -11,7 +11,7 @@
 ARG ENGINE_VERSION=0.8.0
 
 # --- build MCP dist + prod deps (reproducible: committed lockfile + npm ci) ---
-FROM node:22-slim AS mcp
+FROM node:26-slim AS mcp
 WORKDIR /app
 COPY package.json package-lock.json ./
 RUN npm ci --no-audit --no-fund