Resolve latest to the CLI, and cache plugins where kapi actually puts them

[asgeirf]

Audit of setup-kapi turned up two silent bugs. Both are live on @v1 today.

1. version: latest is broken — it resolves to a plugin

The script asked GitHub for releases/latest. But neokapi/neokapi publishes the CLI, the desktop apps, the bowrain server, and every plugin from one repo, and GitHub's "latest" flag lands on whichever was published most recently. Right now that's a plugin:

$ gh api repos/neokapi/neokapi/releases/latest --jq .tag_name
check-v0.1.0

So latest resolved VERSION=check-v0.1.0, then tried to download kapi_check-v0.1.0_linux_amd64.tar.gz from tag vcheck-v0.1.0 → 404. Anyone using the default (or version: latest) is broken until a CLI release happens to be the newest thing published.

latest now resolves the newest stable CLI release itself — tags of the exact shape vX.Y.Z, excluding drafts, prereleases (v1.2.0-rc9), and plugin/app prefixes (check-v*, asr-v*, bowrain-v*). Verified against the live API:

resolver	result
old (releases/latest)	check-v0.1.0 → 404
new	1.1.0 ✅
pinned v1.1.0 / 1.0.0	passes through unchanged ✅

With that fixed, the default version becomes latest rather than a pinned, now-stale 1.0.0 — which is what the README already claimed.

2. The plugin cache pointed at the wrong directory

kapi installs plugins under $XDG_DATA_HOME/kapi/plugins — i.e. ~/.local/share/kapi/plugins on a runner, where XDG_DATA_HOME is unset (cli/plugincmds.go: "…installs to $XDG_DATA_HOME/kapi/plugins/<name>/"). The cache saved ~/.config/kapi/plugins: the config dir, which kapi never writes a plugin to.

So the plugin cache stored nothing, cache-hit was never true, and every run re-downloaded every plugin. Now cached at the real path.

3. Intel macOS fails late instead of early

The CLI ships darwin_arm64 only — there is no darwin_amd64 archive. An x64 macOS runner used to get a 404 on a release asset. platform.sh now says plainly what happened and points at an arm64 runner.

README

• Drops kapi sync (retired — up is the convergence verb).
• Corrects the platform table: macOS is arm64-only.
• Explains why latest can't use GitHub's latest-release flag, so nobody "simplifies" it back.

Verification

All three scripts shellcheck-clean, action.yml parses, and the resolver was run against the live GitHub API (table above). The repo's own test.yml installs on ubuntu/macos/windows on every PR — this exercises the fixed latest path by default.