*: upgrade Go to 1.26 and update static analysis tools

## Enhancement Task

Upgrade active Go version declarations and toolchain references from the Go 1.25 release line to Go 1.26, using the latest Go 1.26 patch release for module directives, and update the static analysis toolchain for Go 1.26 compatibility.

- [ ] Update all Go module directives from Go 1.25.12 to Go 1.26.8.
- [ ] Update GitHub Actions, Docker, build prerequisites, and documentation references from Go 1.25 to Go 1.26 without pinning a patch version where the previous reference did not pin one.
- [ ] Upgrade golangci-lint from v2.6.0 to the latest compatible release (currently v2.13.2).
- [ ] Adapt `.golangci.yml` and the codebase to new checks without changing existing runtime semantics or application logic.
- [ ] Review other Go-dependent static analysis and build tools and update only where required.
- [ ] Run module tidy, build, static analysis, and relevant tests with Go 1.26.8.

Search the repository's Go module directives, GitHub Actions, Docker files, build prerequisites, documentation references, and .golangci.yml for Go 1.25 and golangci-lint v2.6.0. Update the toolchain references and checks as specified, then run module tidy, builds, static analysis, and relevant tests with Go 1.26.8; done means these checks pass without runtime-semantic changes.

Written by the indexing model from the issue text.