fix(#192): HIGH: a read-write sharee can DELETE the owner's entire calendar — the rights pl - #372

RED without the change:
cale_custom_rights.py", line 131, in test_sharee_read_only_access
    self.assertEqual(perm, "rd")
AssertionError: 'r' != 'rd'
- r
+ rd
?  +


======================================================================
FAIL: test_sharee_write_access (test_radicale_custom_rights.TestRadicaleCustomRights.test_sharee_write_access)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/agent-user/Coding/Freeshard/vacation_framework/worktrees/issue-192/server/test/python/test_radicale_custom_rights.py", line 140, in test_sharee_write_access
    self.assertEqual(perm, "rwd")
AssertionError: 'rw' != 'rwd'
- rw
+ rwd
?   +


----------------------------------------------------------------------
Ran 12 tests in 0.372s

FAILED (failures=5)


GREEN with the change:
    1..3
ok 2 - Issue \#201 — Prevent Unauthenticated & Sharee Permanent Calendar Deletion
  ---
  duration_ms: 102.936764
  ...
# Subtest: Issue \#277 — Radicale Custom Rights Case-Insensitive Sharee & Owner Matching
    # Subtest: radicale_custom_rights.py matches sharee and owner usernames case-insensitively
    ok 1 - radicale_custom_rights.py matches sharee and owner usernames case-insensitively
      ---
      duration_ms: 58.600861
      ...
    1..1
ok 3 - Issue \#277 — Radicale Custom Rights Case-Insensitive Sharee & Owner Matching
  ---
  duration_ms: 59.232737
  ...
1..3
# tests 8
# suites 0
# pass 8
# fail 0
# cancelled 0
# skipped 0
# todo 0
# duration_ms 493.409122

............
----------------------------------------------------------------------
Ran 12 tests in 0.374s

OK