Add the schulcloud CLI, and document the split

The CLI talks only to the Pi's /api surface and holds no Schulcloud
credential — only the same bearer token the Claude connector uses. That
is not layering for its own sake: a Schulcloud session dies after two
hours idle and a CLI process lives for seconds, so a CLI with its own
token would be dead most times you reached for it. Routing through the
Pi means one session, one keepalive, one monthly cookie paste.

sync is a one-way mirror, which follows from the data rather than from
scope-cutting: file records are immutable upstream, so there is no
versioning, no conflict resolution and no merge. State is keyed by file
record id with the path as derived output, so an upstream rename moves
the local file instead of duplicating it — verified against the live
server. Verification is size-only because the download endpoint exposes
no ETag and Schulcloud publishes no hash; size still catches the failure
that happens, a truncated download. Downloads land on a .part neighbour
and are renamed, so an interrupted run leaves no half-file that a later
run mistakes for complete. Deletions are reported but not propagated —
a teacher removing a worksheet is no reason to destroy the student's
copy — with --prune to opt in.

what_changed now clamps to the oldest stored generation instead of
refusing, and says it did: "what's new this week" is a reasonable
question to ask a two-day-old index.

Two build bugs caught by the checks rather than by luck: the smoke
harness constructed the app without services, so the index-backed tools
were never exercised; and the Docker build could not see
scripts/copy-assets.mjs, so the image would have shipped without
migrations and silently degraded to live-only.

67 unit tests (9 needing Postgres), smoke green both ways — 34 checks
with an index, 32 without, because graceful degradation is a supported
mode and not a fallback nobody runs.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

docs/CLI.md

@@ -0,0 +1,105 @@
+# The `schulcloud` CLI
+
+Browses and mirrors your Schulcloud files from a laptop, by talking to the
+schulcloud-mcp server on the Pi.
+
+## Why it goes through the Pi
+
+The CLI never talks to Schulcloud. It holds no `jwt` cookie, no Schulcloud
+credential of any kind — only this server's bearer token.
+
+That is not an accident of layering; it solves a real problem. A Schulcloud
+session dies after two hours of inactivity, and a CLI process lives for seconds,
+so a CLI with its own token would be dead most times you reached for it. The Pi
+already keeps one session alive around the clock. Routing through it means one
+session, one keepalive, and one place to paste a fresh cookie once a month.
+
+It also means the laptop cannot accidentally end the server's session: nothing
+here can call logout.
+
+## Setup
+
+```bash
+schulcloud login --server https://mcp.example.org --token <MCP_AUTH_TOKEN> --dir ~/Schulcloud
+```
+
+The token is the same `MCP_AUTH_TOKEN` the Claude connector uses — one token
+guards both surfaces. `login` verifies it before saving, so a typo fails
+immediately rather than on first real use. Config is written to
+`~/.config/schulcloud/config.json` with mode `0600`.
+
+`SCHULCLOUD_SERVER`, `SCHULCLOUD_TOKEN` and `SCHULCLOUD_SYNC_DIR` override the
+file, for CI or one-off invocations.
+
+## Commands
+
+```
+schulcloud status                  how fresh the server's index is
+schulcloud ls [--course <id>] [--long]
+schulcloud get <fileId> [--out <path>]
+schulcloud sync [--dry-run] [--full] [--prune] [--dir <path>] [--jobs <n>]
+schulcloud refresh [--course <id>] [--force]
+```
+
+`ls --long` prints file ids, which is what `get` takes.
+
+`refresh` asks the server to re-read Schulcloud. Pass `--course` when you know
+what changed: that is a handful of requests, where a full re-crawl reads every
+course. The server refuses a repeat within a minute unless you pass `--force`.
+
+## How sync works
+
+It is a **one-way mirror, not a two-way sync**, and that follows from the data
+rather than from laziness: Schulcloud file records are immutable — editing a
+file upstream produces a *new* record — so there is no content versioning, no
+conflict resolution and no merge. "Download what I do not have" is the whole
+algorithm.
+
+Local state lives in `.schulcloud-sync.json` at the root of the sync directory,
+**keyed by file record id with the path as derived output**. That is what makes
+renames cheap: when a teacher renames a board column, the file moves on disk
+instead of being downloaded again under a new name and left duplicated under the
+old one.
+
+What it checks, and why only that:
+
+- **Size**, not a checksum. The download endpoint exposes no `ETag` and
+  Schulcloud publishes no hash, so verifying content would mean re-downloading
+  every file to learn what it already told us. Size reliably catches the failure
+  that actually happens — a truncated or interrupted download — and costs a
+  `stat`.
+- Downloads land on a `.part` neighbour and are renamed into place, so an
+  interrupted run never leaves a half-file that a later run mistakes for
+  complete.
+
+**Deletions are not propagated by default.** A teacher removing a worksheet is
+not a reason to destroy your copy of it; `sync` reports those as "gone upstream,
+kept". Pass `--prune` to actually delete them.
+
+`--dry-run` prints exactly what would happen, writes nothing, and does not
+advance the cursor.
+
+## Cursors
+
+The server's sync cursor is a **crawl generation id**, not a timestamp. This is
+deliberate and measured: `GET /course-rooms/{id}/board` returns the *request
+time* as `updatedAt` for most elements, so a timestamp cursor would report every
+board as changed on every crawl. Comparing generations by identity also detects
+deletions, which no timestamp scheme can.
+
+`--since` on the server API accepts an ISO date for convenience, resolved to the
+nearest generation — but correctness never depends on it.
+
+If the server no longer recognises your stored cursor it returns `409` rather
+than silently treating everything as new, so you are never tricked into
+re-downloading the world. Run `sync --full` deliberately in that case.
+
+## Paths
+
+Mirror paths are `Course/Board/Card/filename`, built by `core/paths.ts`.
+
+Every component of that path originates in Schulcloud — course titles, card
+titles and filenames are all user-supplied upstream — so each is reduced to a
+single safe path component, and the result is re-checked against the sync root
+before anything is written. A file named `../../.ssh/authorized_keys` cannot
+escape, and `sync` refuses such an entry rather than writing it.