feat: add color legend to npm outdated output

[MaxBlack-dev]

Fixes #8850

Summary

Added a color legend to the
pm outdated\ command output to help users understand the meaning of the color-coded package names.

Changes

• Modified \lib/commands/outdated.js\ to add a legend explaining color meanings
• Updated test snapshots to include the new legend in expected output

Legend Details

The legend appears at the bottom of the
pm outdated\ output when terminal colors are enabled:

• Red = Updateable within your version range
• Yellow = Update available but requires semver-major bump

The legend only displays when colors are enabled (\chalk.level !== 0), ensuring it doesn't appear in CI environments or when --no-color\ is used.

Testing

• 58 out of 59 tests pass (1 pre-existing local environment test failure unrelated to changes)
• All snapshots updated correctly
• Legend correctly shows/hides based on color support

[wraithgar]

this.npm.color is what we use to discover if we are outputting in color.

How does this affect --parseable and --json? If folks are expecting to parse this output those lines are going to cause errors.

Does this need to be on every invocation? Is it enough to explain things in the help output?