feat(p7-output-fs): sparse hole preservation (-S), partial retention (-P), fake-super replay; block-size verified; crtimes/stderr -> Impossible/Divergence (Wave B)

- write_all_sparse: skips all-zero runs >= 4096 bytes via lseek(SEEK_CUR) and
  ftruncates the final size, wired into the atomic temp+rename and --inplace
  paths with no wire change (full image already in memory).
- --partial retention: on a save failure after the temp held data, rename the
  already-written temp to the destination path (best-effort; falls through to
  unlink; never retains when --partial is off) so --append/--append-verify can
  resume; tested by forcing futimens EINVAL with an out-of-range nsec.
- --block-size aliases --delta-block; verified config->delta_block_size is
  honored by the delta engine end-to-end (unit + integration tests).
- fake_super_restore_fd: parses and re-applies user.fastsync.stat fd-relative
  (fchown best-effort/non-root skipped, fchmod, futimens); a save under
  --fake-super now both records and re-applies.
- -N/--crtimes and --stderr=client promoted to a new 'Impossible/Divergence'
  status bucket (Summary: 136/2/4/3/2 = 147).
- cppcheck/clang-format clean; unit 37/37; integration 407 passed.

src/client/client_cli.c

@@ -1079,7 +1079,7 @@ int parse_args(Config* config, int argc, char* argv[], int* positional_args,
       if (config_add_pattern(&config->include_patterns, &config->include_count, argv[++i],
                              "--include") != 0)
         return -1;
-    } else if (opt_is(argv[i], "--delta-block", NULL)) {
+    } else if (opt_is(argv[i], "--delta-block", "--block-size")) {
       if (i + 1 >= argc) {
         log_message(LOG_LEVEL_ERROR, "missing argument for %s", argv[i]);
         return -1;