Align Go modules and CI on Go 1.26.8

[augmentcode]

Summary

• Set the root module, Tsunami SDK, all eight demo modules, and the scaffold module template to Go 1.26.8.
• Make TestDriver builds, release builds, CodeQL, and Copilot setup read their Go version from the root go.mod, eliminating duplicate pins and future version drift.
• Remove the unused Go version setting from the TestDriver run workflow. Dependency versions and historical release notes are unchanged.

Why

The TestDriver packaging step installs Go 1.25.6 while the root module requires Go 1.26.0. With GOTOOLCHAIN=local, packaging exits before TestDriver can run. This aligns the repository on the requested patched Go 1.26 release.

Validation

Performed using Go 1.26.8:

• Passed: go test ./cmd/generateschema ./pkg/wconfig ./pkg/util/utilfn ./pkg/util/shellutil.
• Passed: root and Tsunami go mod tidy -diff; Tsunami checked in a temporary tracked-source copy to avoid local generated scaffold files.
• Passed: root and Tsunami go mod verify.
• Passed: workflow YAML parsing, version-consistency assertions for all ten modules plus the template and all four Go setup steps, Prettier checks, and git diff --check.
• Tsunami's full suite has a pre-existing TestJsonH failure (data1: int); reproduced identically on unchanged source with Go 1.26.8. All remaining Tsunami package tests pass with that single test excluded.

Windows packaging/TestDriver and the full release build were not run locally; CI must confirm those paths.

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Pull Request opened by Augment Code

[coderabbitai]

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