Update Go versions and golangci-lint action in CI

[thomas-vilte]

Description

I updated the Go versions used in the CI workflows from 1.21, 1.22, 1.23 to 1.25, 1.26. This includes updating the golangci-lint GitHub Action from v6 to v9 and explicitly pinning the linter version to v2.12.2 to ensure compatibility with Go 1.25+.

Additionally, I refactored string building in several internal AI and service files, replacing sb.WriteString(fmt.Sprintf(...)) with fmt.Fprintf(&sb, ...). This change improves consistency and can offer minor performance benefits.

Fixes #

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

The changes to the CI workflows are verified by the successful execution of the workflows themselves on this branch. The updated Go versions and golangci-lint action will run as part of the standard CI process.

• Unit tests
• Integration tests
• Manual test: CI workflows execution

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Test Plan & Evidence

Suggested Manual Verification

• API/Backend: Attach JSON response or logs as evidence of correct behavior
• Performance: Ensure no significant latency increase
• Unit Tests: Run go test ./... and ensure all tests pass
• No Regressions: Verify that related features still work as expected