fix(extensions): show extension ID in list output

[mbachorik]

Summary

• Display extension ID in specify extension list output

Problem

When extension names are ambiguous, users are told to use the extension ID:

Please rerun using the extension ID:
  specify extension <command> <extension-id>

But specify extension list didn't show the ID, forcing users to inspect .specify/extensions/registry.json manually.

Solution

Add the ID on a separate line (dim style) below the extension name:

  ✓ Jira Integration (v1.2.0)
     speckit/jira
     Integrate Jira issues with spec-kit workflows
     Commands: 3 | Hooks: 1 | Status: Enabled

Test plan

• Run full test suite (301 tests pass)
• Ruff linter passes
• Added TestExtensionListCLI::test_list_shows_extension_id test

Fixes #1832

🤖 Generated with Claude Code

[Copilot]

Pull request overview

Improves the UX of extension management by making the installed extension ID discoverable directly in specify extension list, aligning the list output with guidance shown in ambiguous-name error flows.

Changes:

• Print each installed extension’s id on a separate (dim) line beneath the extension name in specify extension list.

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[Copilot]

Pull request overview

Updates the specify extension list CLI output to include each installed extension’s ID, making it easier for users to act on extensions when names are ambiguous (as suggested by existing CLI error guidance).

Changes:

• Print the installed extension id on a dimmed line directly under the extension name in specify extension list.
• Add a CLI integration test asserting the list output includes the extension ID (plus name/version).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/specify_cli/__init__.py	Adds a new output line in extension_list() to print ext["id"] beneath the extension name.
tests/test_extensions.py	Adds TestExtensionListCLI::test_list_shows_extension_id to validate the new list output includes the extension ID.

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