Fixes #14647

Description

gh skill update --help previously stated that --force "does not remove extra files added locally."
However, swapDirectoryContents replaces the installed directory wholesale with the staged upstream skill contents for both --force and standard version updates, so any extra locally-added files in the skill directory are discarded whenever an update is applied (as asserted by the update tests in pkg/cmd/skills/update/update_test.go:L778-L780).

This updates cmd.Long and the --force --all example description to accurately state that applying an update replaces the installed directory's contents with the upstream skill, discarding local modifications and additional files. It also clarifies that --force specifically re-downloads and replaces skills when the remote version matches the local tree SHA.

How did you test this change?

I ran go test -v -run TestNewCmdUpdate_Help ./pkg/cmd/skills/update with the updated assertions and verified it passed cleanly.

I then ran go run ./cmd/gh skill update --help with the built binary and confirmed the rendered help text:

Applying an update replaces the installed skill directory's contents
with the upstream skill, discarding local modifications and additional files.

With `--force`, re-downloads and replaces skills even when the
remote version matches the local tree SHA.

and the updated example line:

  # Re-download all skills even if up to date (discarding local modifications)
  $ gh skill update --force --all

Key points

• Help text correction only: The underlying update behavior is intentional and relied upon to clean stale files during updates. Only the documentation was incorrect.
• Clear separation: Explains the directory replacement rule for all updates generally, and restricts the --force description to what the flag actually controls (updating even when the remote tree SHA has not changed).

Notes for reviewers

The change is in pkg/cmd/skills/update/update.go with corresponding assertions added in TestNewCmdUpdate_Help in pkg/cmd/skills/update/update_test.go.

Authorship and follow-up

Who wrote this:

• A human wrote it.
• An agent wrote it under close human direction.
• An agent wrote it independently, and no human has guided the implementation beyond the initial prompt.

Who answers review comments:

• @rajpreetcodes will read and reply directly. Name the account.
• An agent will draft replies and @rajpreetcodes will read them before they are posted.
• Nobody has explicitly committed to replying.