Add runtime regex notification checks

[Da7-Tech]

Fixes #2.

Summary

• Adds --checks / --check-config for runtime JSON-configured regex notification checks.
• Accepts either a top-level JSON array or an object with checks: [].
• Supports field, regex, alert/message, and optional ignore_case / case_insensitive.
• Supports domain fields, DNS fields (type, info, rdata, ttl), HTTP metadata (http_code, code_string, content_length), and response body.
• Runs body checks in memory during probing and does not write response bodies to the JSON output.
• Wires checks through both HTTP execution paths: deferred HTTP probing and DNS-then-HTTP probing.
• Documents the config format in the README.

Verification

• git diff --check
• c++ -std=c++17 -O0 -I dooked/include -I dooked/json/single_include -I dooked/spdlog/include -c dooked/source/utils/regex_checks.cpp -o /tmp/regex_checks.o
• c++ -std=c++17 -O0 -I dooked/include -I dooked/json/single_include -I dooked/spdlog/include -c dooked/source/utils/io_utils.cpp -o /tmp/io_utils.o
• Standalone smoke test compiled and ran load_regex_checks, run_result_checks, and run_body_checks, producing matches for domain, DNS type, HTTP code, and body checks.

I could not run the repository's full CMake build locally because this machine does not have cmake or Boost headers installed. I initialized the repo submodules and verified the new check parser/runner path separately.

AI assistance disclosure: prepared with Codex and manually reviewed before submission.

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