Initial schulcloud-mcp server

Read-only MCP server exposing a Schulcloud account to Claude: courses,
column boards, lessons, tasks, and file downloads with text extraction.

The API surface was verified against the live instance rather than
inferred from upstream source, which changed several design decisions:

- The `jwt` cookie works verbatim as `Authorization: Bearer` and lasts 30
  days, so there is no cookie jar and no refresh-session timer.
- Course contents live at /api/v3/course-rooms/{courseId}/board; there is
  no GET /api/v3/courses/{id}.
- Files are a separate service (/api/v3/file/*) with its own OpenAPI doc.
- Board file elements carry no file id; attachments are resolved by
  listing files-storage with parentType=boardnodes and the element id.

Read-only by construction: every client method is a GET, including the
api_get escape hatch. The endpoint is internet-facing by necessity, so a
leaked token being unable to act as the user is the key safety property.

Deploys as a container behind the Pi's existing Caddy, guarded by a
constant-time bearer check. Stateless — no database.

Verified: 28 unit tests, plus a 30-check end-to-end run driving a real
MCP client over Streamable HTTP against the live account.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Dockerfile

@@ -0,0 +1,41 @@
+# syntax=docker/dockerfile:1
+
+# Build stage: full dependency tree, compile TypeScript to dist/.
+FROM node:22-alpine AS build
+WORKDIR /app
+COPY package.json package-lock.json ./
+RUN npm ci
+COPY tsconfig.json ./
+COPY src ./src
+RUN npm run build
+
+# Prune to runtime dependencies only, in its own stage so the build tree
+# (typescript, @types) never reaches the final image.
+FROM node:22-alpine AS deps
+WORKDIR /app
+COPY package.json package-lock.json ./
+RUN npm ci --omit=dev && npm cache clean --force
+
+FROM node:22-alpine AS runtime
+WORKDIR /app
+ENV NODE_ENV=production
+
+# Every extractor is pure JavaScript, so the runtime image needs no build
+# toolchain — just a signal-forwarding init so SIGTERM reaches node.
+RUN apk add --no-cache tini
+
+COPY --from=deps  /app/node_modules ./node_modules
+COPY --from=build /app/dist ./dist
+COPY package.json ./
+
+# node:alpine ships an unprivileged `node` user; the process never writes to disk.
+USER node
+
+EXPOSE 8080
+ENV PORT=8080 BIND_HOST=0.0.0.0
+
+HEALTHCHECK --interval=30s --timeout=5s --start-period=10s --retries=3 \
+  CMD node -e "fetch('http://127.0.0.1:'+(process.env.PORT||8080)+'/healthz').then(r=>process.exit(r.ok?0:1)).catch(()=>process.exit(1))"
+
+ENTRYPOINT ["/sbin/tini", "--"]
+CMD ["node", "dist/bin/http.js"]