* fix(#2831): expand HOME in OpenCode skill/template paths
OpenCode does not shell-expand $HOME in @file references on any platform —
the literal `@$HOME/...` path is resolved relative to the config command/
dir, producing `command/$HOME/...` (file not found). The previous fix for
#2376 only guarded Windows; extend to all platforms.
Closes#2831
* test(#2831): assert behavior via exported computePathPrefix, not source grep
Addresses CodeRabbit review on PR #2842:
- Extracts pathPrefix logic into a named, test-exported computePathPrefix
helper in bin/install.js (no behavior change at the call site).
- Rewrites bug-2376 and bug-2831 regression tests to call the exported
function directly instead of regex-matching install.js source text,
per the repo's no-source-grep testing standard.
- Wraps temp-dir test setup in try/finally so cleanup runs on assertion
failures (no leaked tmp dirs).
a7f83ee663