Merge pull request #11 from SteveParson/fix/docker-scratch-assimilate

fix(docker): assimilate APE binary for scratch image, expand test cov…

add missing package

add cosmopolitan libc port using mbedtls and cosmocc

produces a single actually portable executable (APE) that runs on
linux, macos, windows, freebsd, openbsd, and netbsd from one binary.

replaces bearssl with upstream mbedtls 2.28.8 (vendored as submodule),
builds with cosmocc toolchain which is auto-downloaded by the makefile.
embeds root CA certificates directly in the binary.

bot logic (gateway lifecycle, websocket framing, json parser, heartbeat
with exponential backoff retry) adapted from the main codebase into a
flat layout under cosmo/ (~1000 lines across 4 .c files).

also adds a cosmo build job to CI and includes the APE in releases.

add docker build back, push cosmo image to ghcr

clang format and tidy, fix docker build

add clang-format and clang-tidy linting with CI integration

- add .clang-format (LLVM style, 4-space indent, 100 col limit)
- configure .clang-tidy with targeted check suppressions
- apply 142 clang-tidy auto-fixes (braces, isolated declarations, parens)
- reformat all source with clang-format v21
- add make lint target with cosmocc download guard
- pin LLVM 21 in CI lint job via apt.llvm.org
- suppress getrandom implicit-declaration for non-cosmocc clang-tidy

promote cosmo port to root, drop autotools and bearssl, add tests

Add debug logging for message send failures

fix: docker uri

Add heartbeat retry with exponential backoff, fix lint, update README