feat(cli): add --dry-run mode

[Zai69]

Goal

Add a --dry-run option to the main CLI command so users can preview what would be installed without writing anything to disk.

Acceptance Criteria

• uipro --dry-run does not write any files
• CLI prints the list of target files/actions
• Exit code is 0
• Manual test usage is documented in README

[mrgoonie]

Summary: This is a valid CLI feature request, and there was already an attempted implementation in PR #292, but that PR was closed unmerged.nnDecision: accepted / needs implementationnnEvidence:n- The issue defines clear acceptance criteria: no writes, planned target files/actions, zero exit code, and README usage docs.n- PR #292 proposed uipro init --dry-run and documented manual verification, but it is closed and was not merged.n- Current maintainer queue still has no merged dry-run implementation found from the issue/PR search.nnNext step: reopen or recreate the dry-run implementation as a focused CLI PR, keeping the scope to previewing install actions and proving that no files are written during dry-run.