feat(sender): --ignore-missing-args / --delete-missing-args CLI and files-from preflight

New flags parse onto the config; --delete-missing-args implies
--ignore-missing-args (order-independent) and does NOT imply --delete (rsync:
independent of other delete processing). The files-from preflight now classifies
listed-but-missing entries instead of hard-failing: under the flags each is
skipped (logged + counted, never silent) and the run succeeds for the rest,
including the all-missing case; an empty list stays a hard error. Under
--delete-missing-args the missing entries' destination mirrors (bare relative
path with -R, full source mirror otherwise) ride the manifest's third section in
both the single-threaded and -m senders; --dirs listed-but-missing entries are
skipped in the scanner.

src/client/client_cli.c

@@ -460,6 +460,8 @@ static const OptionEntry OPTION_TABLE[] = {
     {"--ignore-errors", NULL, OPT_FLAG, offsetof(Config, ignore_errors)},
     {"--force", NULL, OPT_FLAG, offsetof(Config, force_delete)},
     {"--prune-empty-dirs", NULL, OPT_FLAG, offsetof(Config, prune_empty_dirs)},
+    {"--ignore-missing-args", NULL, OPT_FLAG, offsetof(Config, ignore_missing_args)},
+    {"--delete-missing-args", NULL, OPT_FLAG, offsetof(Config, delete_missing_args)},
 
     {"--source-dir", NULL, OPT_STRING, offsetof(Config, send_directory)},
     {"--dest-dir", NULL, OPT_STRING, offsetof(Config, receive_root_directory)},
@@ -739,6 +741,12 @@ int parse_args(Config* config, int argc, char* argv[], int* positional_args,
           entry->offset == offsetof(Config, delete_delay) ||
           entry->offset == offsetof(Config, delete_after))
         config->use_delete = true;
+      /* --delete-missing-args implies --ignore-missing-args (missing entries
+         are skipped for deletion instead of failing the run).  The implication
+         is order-independent because it is applied over the final parsed
+         config. */
+      if (entry->offset == offsetof(Config, delete_missing_args))
+        config->ignore_missing_args = true;
       continue;
     }