fix: address low/informational sec-parser follow-ups

- client_cli: capture errno before output_escape() in
  read_patterns_from_file() so an over-long line is still reported as
  EFBIG instead of the (possibly malloc-clobbered) errno.
- file_list: guard string_list_add() capacity doubling against
  overflow (capacity > INT_MAX / 2), matching filter_rule_list_add();
  callers already surface the false as a memory-allocation error.
- compression: ZSTD_isError() is true for ZSTD_CONTENTSIZE_UNKNOWN,
  which made the 3x unknown-size fallback dead code.  Test the
  CONTENTSIZE_ERROR/UNKNOWN sentinels explicitly so unknown-size frames
  reach the estimate path (still bounded by the existing hard limit)
  while invalid frames are rejected.  Known-size frames and the 100 MB
  ceiling/overflow checks are unchanged.
- tests: add an unknown-content-size-frame decompression test.

Tests: ./build/tests and ./build-asan/tests all pass (42/42);
clang-format + cppcheck clean.

src/shared/file_list.c

@@ -23,6 +23,8 @@ static void string_list_destroy(StringList* list) {
 
 static bool string_list_add(StringList* list, const char* text) {
   if (list->count == list->capacity) {
+    if (list->capacity > INT_MAX / 2)
+      return false;
     int new_cap = list->capacity > 0 ? list->capacity * 2 : 16;
     char** grown = realloc(list->items, (size_t)new_cap * sizeof(char*));
     if (!grown)