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>

.env.example

@@ -52,6 +52,12 @@ DATABASE_URL=postgresql://schulcloud:schulcloud@postgres:5432/schulcloud
 # three extra requests per task on a full crawl, so it is off by default.
 # INDEX_PERSONAL_FILES=false
 
+# Also walk the file manager ("Dateien") when crawling: Kurs-Dateien for every
+# course, plus Persönliche, Team- and Geteilte Dateien on a full crawl. Many
+# teachers keep their material only there, so this is on by default. One page
+# load per folder — about 160 on a 26-course account.
+# INDEX_FILE_MANAGER=true
+
 # How often to re-crawl on a timer, in ms. Default 21600000 (6h). 0 = on demand
 # only. A re-crawl of unchanged content downloads nothing, because Schulcloud
 # file records are immutable.