Add Readme section to get_module_details output

[huynhsontung]

get_module_details was not surfacing the root README from the registry API response. This adds the README to the output, filtered to remove sections (inputs, outputs, dependencies, resources) already represented as structured data — consistent with how get_private_module_details handles it.

Changes

• pkg/utils/utils.go — Promoted removeReadmeSections from tfe package to shared, exported RemoveReadmeSections utility to avoid duplication
• pkg/tools/registry/get_module_details.go — Added ### Readme section at the end of unmarshalTerraformModule, populated from Root.Readme and cleaned via utils.RemoveReadmeSections; skipped when empty
• pkg/tools/tfe/get_private_module_details.go — Replaced local removeReadmeSections call with utils.RemoveReadmeSections; removed now-unused regexp import
• Tests — Added TestRemoveReadmeSections in utils_test.go; added TestUnmarshalModuleSingular_WithReadme and TestUnmarshalModuleSingular_EmptyReadme in get_module_details_test.go

PCI review checklist

• I have documented a clear reason for, and description of, the change I am making.

• If applicable, I've documented a plan to revert these changes if they require more than reverting the pull request.

• If applicable, I've documented the impact of any changes to security controls.

  Examples of changes to security controls include using new access control methods, adding or removing logging pipelines, etc.

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