Contributor setup for Swift 6.4 on Ubuntu 26.04

Almanac 0.12.2 changes nothing for apps using it: the TypeScript, Swift, and Kotlin libraries and every result are the same as 0.12.1. It updates the setup for people building Almanac from source, and it is the first release published from GitHub's Ubuntu 26.04 runners.

• Local Swift development uses one Swift 6.4.0 pin on macOS and Linux, and needs mise 2026.9.11 or newer, which installs the native Ubuntu 26.04 toolchain. #98 #101
• The contributor guide links to the shared Open Waters Swift toolchain guidance, including how to recover from an incompatible installed toolchain. #102

npm install @openwaters/almanac@0.12.2

.package(url: "https://github.com/openwatersio/almanac.git", exact: "0.12.2")

Kotlin consumers can pin the v0.12.2 source checkout using the installation guide. No Maven artifact is published.

Release preparation: #104.

Full changelog.