GeezerVison

The repository has several Go version pins that should stay aligned so local development, CI, module metadata, and Docker builds use the same patch release.

Update the root and vendored lib module directives, mise.toml, the vendored-lib generation template, and the Docker builder image to Go 1.26.3. Remove .tool-versions so mise.toml is the single checked-in tool version source. The Docker builder image remains pinned by digest for reproducible builds.

Test Plan

• go version
• go test ./...
• cd lib && go test ./...