chore: pin golangci-lint via .tool-versions and tune goconst config

[Davidnet]

Summary

• Tune goconst config in .golangci.yml:
  • ignore-tests: true so test-file repetitions don't push production code over the threshold (test files were already excluded from being reported, but their occurrences still leaked into the count).
  • ignore-string-values: '^(limit|success)$' — these are JSON response keys, not magic values worth extracting.
• Replace mise.toml with .tool-versions as a single source of truth for go and golangci-lint versions.
• Wire the CI golangci-lint-action to version-file: .tool-versions so CI and local stay in sync (without this, the action defaults to installing latest).

Result: golangci-lint run goes from 11 issues to 0 with no production source changes, and the linter version is pinned identically locally and in CI.

Test plan

• mise install picks up go 1.25.6 and golangci-lint 2.12.2 from .tool-versions
• mise exec -- golangci-lint run reports 0 issues
• CI Go Lint job uses golangci-lint 2.12.2

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[Copilot]

Pull request overview

This PR aligns local and CI tooling by pinning golangci-lint (and Go for local dev) via .tool-versions, and reduces goconst noise by tuning its configuration so production linting isn’t affected by repetitions in test files or common JSON response keys.

Changes:

• Add .tool-versions (Go + golangci-lint) and remove mise.toml to consolidate version pinning.
• Update .golangci.yml goconst settings (ignore-tests, ignore-string-values).
• Configure the GitHub Actions golangci-lint-action to use .tool-versions via version-file.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
mise.toml	Removed in favor of .tool-versions as the version source.
.tool-versions	New pinned versions for go and golangci-lint for local tooling.
.golangci.yml	Tunes goconst behavior to reduce irrelevant findings.
.github/workflows/lint-and-test.yml	Pins CI golangci-lint install to .tool-versions for consistency.

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