feat(delete): default --delete to rsync delete-during; add --delete-commit

- plain --delete with no timing flag now selects delete-during (progressive
  deletion, matching rsync and avoiding the full old+new tree peak)
- new long-only FastSync --delete-commit restores the old atomic behavior
  (delete only after the whole transfer succeeds); timing-identical to
  --delete-after, implemented via the same wire bool
- timing flags are mutually exclusive; --delete-commit conflicts with other
  timings; --delete-before/--delete-during rows reworded per Phase-0 probes
- CHANGELOG migration note; tally unchanged 116/14/27

tests/integration/test_differential_parity.py

@@ -241,6 +241,9 @@ _CASES = [
            server_args=DELETE, ref="--delete-delay"),
     H.Case("delete_after", "basic", ["-a", "--delete-after"], seed=seed_extras,
            server_args=DELETE, ref="--delete-after"),
+    H.Case("delete_commit", "basic", ["-a", "--delete-after"], seed=seed_extras,
+           fastsync_flags=["-a", "--delete-commit"], server_args=DELETE,
+           ref="FastSync-only --delete-commit == rsync --delete-after"),
     H.Case("delete_excluded", "filters",
            ["-a", "--delete", "--delete-excluded", "--exclude=*.log"],
            seed=seed_delete_excluded, server_args=DELETE, ref="--delete-excluded"),
@@ -255,7 +258,7 @@ _CASES = [
     H.Case("filter_protect", "filters",
            ["-a", "--delete", "--filter=P *.log"],
            seed=seed_filter_protect, server_args=DELETE, ci=True,
-           ref="--filter P/--protect receiver-side delete protection"),
+           ref="--filter P/--protect receiver-side delete protection (default during)"),
     H.Case("filter_protect_during", "filters",
            ["-a", "--delete-during", "--filter=P *.log"],
            seed=seed_filter_protect, server_args=DELETE, ci=True,
@@ -264,6 +267,10 @@ _CASES = [
            ["-a", "--delete-delay", "--filter=P *.log"],
            seed=seed_filter_protect, server_args=DELETE, ci=True,
            ref="--filter P/--protect under --delete-delay"),
+    H.Case("filter_protect_after", "filters",
+           ["-a", "--delete-after", "--filter=P *.log"],
+           seed=seed_filter_protect, server_args=DELETE, ci=True,
+           ref="--filter P/--protect under the whole-tree --delete-after commit"),
 
     # --- relative / dirs --------------------------------------------------
     H.Case("relative_general", "basic", ["-a", "-R"], layout=H.MIRROR_ABS,