Summary

• Adds TechStackTerraform detection by scanning for .tf files in the repository root
• Adds a dedicated vigilante-issue-implementation-on-terraform skill with idiomatic Terraform workflow guidance (fmt, validate, init, lint, plan safety, state security, credentials, provider/module hygiene, mixed-language scoping)
• Adds Terraform security guidance to the prompt builder covering formatting, validation, linting, state security, credentials, provider hygiene, plan safety, and mixed-language repositories
• Adds skill selection logic: Terraform skill is selected for traditional Terraform-only repos; Go/GitHub Actions/Docker take priority when present; monorepo skills take priority for monorepo shapes
• Preserves all existing Docker detection, skill, security guidance, and tests unchanged

Test plan

• TestClassifyTerraformRepoFromTFFiles — detects .tf files as Terraform tech stack
• TestClassifyNonTerraformRepoHasNoTerraformTechStack — no false positives
• TestClassifyTerraformAndGoRepoDetectsBoth — dual-stack detection
• TestIssueImplementationSkillSelectsTerraformForTerraformRepo — correct skill selection
• TestIssueImplementationSkillPrefersGoOverTerraformForDualStack — priority ordering
• TestIssueImplementationSkillPrefersMonorepoOverTerraform — monorepo takes precedence
• TestSecurityGuidanceForTerraformRepo — all guidance sections present
• TestTerraformMixedLanguageGuidanceIncludedForGoAndTerraform — mixed-language section injected
• TestTerraformMixedLanguageGuidanceOmittedForTerraformOnly — no mixed-language for pure Terraform
• TestTerraformSkillIsBundled — skill asset embedded
• TestTerraformSkillCoversRequiredGuidanceAreas — skill content validated
• All existing Docker tests continue to pass unchanged

Closes #365