feat(skills): add --force/-f to skills install to reinstall installed skills

[tallguys]

Problem

clime skills install <owner/repo> filters already-installed skills out of the selection picker (installFromRepo), so there's no way to reinstall/refresh a skill you already have from that command — you have to uninstall it first, then install and re-pick it.

The interactive Update installed skills action does exist, but it's only reachable by running clime skills install with no args and drilling into the source→action menu; it isn't available directly from install <repo>.

Change

Add --force / -f to skills install:

• With a repo arg, already-installed skills are kept in the picker (labelled (reinstall)) instead of being filtered out, and installing overwrites their files.
• Without --force, behavior is unchanged (installed skills are still filtered).
• The interactive source menu and runSkillsSourceAction signatures are untouched, so existing interactive tests are unaffected.

$ clime skills install owner/repo --force
✓ Found N skill(s) in "owner/repo"
? Select skills to install (space to toggle, enter to confirm)
  ○ some-skill — ... (reinstall)
  ○ another-installed-skill — ... (reinstall)
  ○ a-new-skill — ...
  ...

Implementation notes

• The candidate-filtering logic is extracted from installFromRepo into a pure selectInstallCandidates(repoSkills, manifest, force) helper so the force branch is unit-testable without the network/git path.
• Reinstall relies on the existing overwrite behavior of installFiles (writes files in place) and Manifest.AddSkill (upsert by name), so no duplicate manifest entries.

Tests

New cmd/skills_force_test.go:

• default mode filters out installed skills;
• --force keeps installed skills and marks them (reinstall), without mislabelling not-installed ones;
• empty repo yields no candidates.

go build ./..., go vet ./..., and go test ./... all pass. Also verified end-to-end against a real repo: install <repo> -f now lists the installed skills (marked (reinstall)) that plain install <repo> hides.

🤖 Generated with Claude Code