GitHub Actions workflow (.github/workflows/release.yml):
- Triggers on tag push (v*.*.*)
- Builds all 27+ environments in 4 parallel matrix groups
  (RISC-V, Xtensa-S3, Xtensa-ESP32, Xtensa-other)
- Collects named binaries (firmware_<env>_<version>.bin)
- Creates GitHub Release with all binaries + SHA256 checksums
- Pre-release flag for -rc and -beta tags
- PlatformIO cache for faster rebuilds

Firmware versioning:
- extra_script.py: embeds git describe version in binary name
  and as FIRMWARE_VERSION compile-time define
- Version shown in serial boot banner for all firmware types
- Local builds show git hash (e.g., e8e22e3-dirty)
- Tagged builds show semver (e.g., v1.0.0)

CHANGELOG.md: v1.0.0 initial release notes covering all features,
supported hardware, path capacity, and known limitations.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>