fix(cases): keep deleted workspaces deleted, cap pastCap, scope stalls to network mounts

- applyWorkspaceHooks: an "unknown" probe that is not near a stalled path
  (refused by the stall cap, or an unexpected stat error) no longer reads as
  "go ahead". It checks existence with pathExistsForWrite first, so a deleted
  workspace is not recreated by the mkdir -p in ensureCodemanHooks.
- pastCap gets a hard ceiling, PATH_PROBE_STALL_CEILING = UV_THREADPOOL_SIZE
  (default 4) minus one, so explicit requests against several dead paths can
  never take the last libuv worker. The bulk cap now defaults to one below the
  ceiling (2 with the default pool), leaving a slot for an explicit request.
- A stall widens to its mount only for network and FUSE filesystem types read
  from /proc/self/mounts; on a local mount (a path typed under a local /home
  that reaches a NAS through a symlink) it narrows to the stalled path.
- GET /api/cases/:name probes CLAUDE.md with pastCap, like the folder probe.
- Comment in config/path-probe.ts describes the mount-scoped stall.

test/routes/case-routes.test.ts

@@ -779,6 +779,8 @@ describe('case-routes', () => {
       expect(res.statusCode).toBe(200);
       expect(JSON.parse(res.body).data).toMatchObject({ name: 'healthy-local' });
       expect(JSON.parse(res.body).data.unreachable).toBeUndefined();
+      // Its CLAUDE.md is probed the same way as its folder, so it is not misreported missing.
+      expect(JSON.parse(res.body).data.hasClaudeMd).toBe(true);
     });
 
     it('answers a local case it cannot read with a non-NOT_FOUND error', async () => {