feat(release): zap things-cli cache on cask uninstall

[ryanlewis]

Summary

Adds a zap: stanza to the Homebrew cask so a full uninstall (brew uninstall --zap things) cleans up ~/Library/Caches/things-cli — the last-list cache that backs things complete 1-style indices.

Standard Homebrew behaviour: zap is opt-in via --zap (or brew zap things separately), so plain brew uninstall things still leaves the cache alone. That's deliberate — uninstall + reinstall (or switching between brew and a local dev build that reads the same cache path) shouldn't blow away state.

Generated cask diff

   binary "things"

   postflight do
     # ...quarantine xattr removal...
   end

+  zap trash: [
+      "~/Library/Caches/things-cli",
+    ]

Test plan

• goreleaser check passes
• goreleaser release --snapshot --clean --skip=publish generates a cask with the zap trash: [...] block
• After merge + the next release tag: brew install ryanlewis/tap/things, then brew uninstall --zap things, confirm ~/Library/Caches/things-cli is moved to Trash