fix: parent-scoped file selection; never mutate the pySim model

pySim's lchan.select() resolves names against global selectables (self +
parent chain + MF children + applications) and falls back to probe_file(),
which blindly SELECTs an unknown FID and permanently injects a dynamically
named DF.XXXX/EF.XXXX into the running filesystem model. Probing a whole tree
or scanning a snapshot with custom files therefore polluted the model, made
tree branches show children of the wrong object, and could persist phantom
files into snapshots.

- server: new _select_with_parent()/_select_path() walk the requested parent
  path (new parent_path field, parent_sel kept as legacy fallback) strictly
  through the model and call lchan.select_file() only; model-unknown 4-hex
  segments are probed only with allow_probe and the temporary child pySim
  adds is detached again via the cleanup callable that the four handlers
  (/api/tree|select|read|write) now run in a finally block
- frontend: getParentPath() builds the segment chain (MF, ADF names, FIDs)
  and all tree/select/read/write bodies plus the snapshot/profile walker send
  parent_path; allow_probe is set only for custom files; the blind retries
  in the file manager were dropped
- tests: tests/test_select_scope.py (duplicate-FID resolution, no APDU for
  unknown non-custom files, probe+detach, model unchanged); fs_load/fs_probe
  assertions for parent_path and allow_probe; docs/api.md and AGENTS.md
  document the contract; SW cache v117 -> v118.

frontend/sw.js

@@ -1,4 +1,4 @@
-const CACHE = 'otaman-v117';
+const CACHE = 'otaman-v118';
 const URLS = [
   'index.html',
   'help.html',