Browse the file manager ("Dateien") as a filesystem

Many teachers never use topics or boards; their material sits in the
course's file area, and the tools answered "0 files" for courses holding
dozens of worksheets — 21 of 26 courses on the live account. Persönliche,
Kurs-, Team- and Geteilte Dateien live in the legacy file store, not in
files-storage, and its service is not in the public ingress. The only way in
is the legacy client: HTML listings, and GET /files/signedurl for a
pre-signed download.

core/legacy-files.ts turns that into one path tree — /my, /courses/<course>,
/teams/<team>, /shared — resolving names that contain "/", ids anywhere in a
path, and wrong or ambiguous names with a message saying what is there. A
listing that does not parse throws; it never reads as an empty folder.

Some of the legacy client's GET routes write (GET /files/share/ mints a
share token), so getFileManagerPage allows only the listing routes, by
pattern. Signed URLs are fetched with no credentials and must be https.

- MCP: fs_list, fs_tree, fs_find and fs_read; get_course lists course files.
- CLI: schulcloud fs ls, tree, find and get, recursive and resumable.
- API: /api/fs/list, tree, find and file.
- Index: the crawl walks the file manager (INDEX_FILE_MANAGER, on by
  default), so search covers the text inside those files and sync mirrors
  them under <course>/Kurs-Dateien.

The local instance gains a fixture for all four areas. It needed a loopback,
so signed URLs open from the host, and a pre-created bucket, since MinIO
does not implement PutBucketCors.

135 tests. Smoke 55/55 live; 57/57 and 55/55 on the local instance.

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

docs/LOCAL.md

@@ -103,9 +103,9 @@ node dist/bin/cli.js sync
 ## Run the test suites
 
 ```bash
-npm test              # 58 offline tests
+npm test              # 135 offline tests
 npm run smoke         # end-to-end against the live instance, live-only mode
-DATABASE_URL=… npm run smoke    # end-to-end with the index (34 checks)
+DATABASE_URL=… npm run smoke    # end-to-end with the index (57 checks)
 ```
 
 Store tests need a database and skip without one: