fix(cli): expand "~/" home shorthand on Windows

[LukeTheoJohnson]

Problem

On Windows, the ~/ home shorthand is not expanded, so the CLI treats a literal ~ as a real path segment.

expandHome() in src/utils/resolve-home.ts only matched `~${path.sep}`. On Windows path.sep is \, so that check is ~\. The portable ~/ spelling, the one users and config files write across platforms, falls through unmatched and is returned verbatim.

Because expandHome backs resolveTargetHome / resolveCodexHome, the unexpanded value reaches convert, install, and cleanup through --output, --codex-home, --pi-home, CODEX_HOME, and OPENCODE_CONFIG_DIR. The result is a bogus ~ directory created in the working tree instead of a path under the user's home.

This is Linux/macOS-invisible: there path.sep is /, so ~/ already matches. CI runs on ubuntu-latest only, which is why it was not caught.

Root cause / evidence

Reproduced with the real function on Windows (path.sep === "\\", os.homedir() === C:\Users\lukej):

expandHome("~")         -> "C:\Users\lukej"          (ok)
expandHome("~/.codex")  -> "~/.codex"                (BUG: unexpanded)
expandHome("~\.codex")  -> "C:\Users\lukej\.codex"   (native separator already worked)

Fix

Match ~/ in addition to the native separator:

if (value.startsWith("~/") || value.startsWith(`~${path.sep}`)) {
  return path.join(os.homedir(), value.slice(2))
}

Surgical by design: POSIX behaviour is unchanged. On POSIX ~\foo still passes through untouched (backslash is a legal filename character there); only Windows ~/x handling changes.

Tests

Adds tests/resolve-home.test.ts:

• ~/.codex and ~/sub/dir expand to a home-joined path on every platform (the regression guard: red on Windows before this change, green after).
• the native-separator form and bare ~ still expand.
• ~foo, relative, and absolute paths pass through unchanged.

Verification on Windows:

• The forward-slash test fails on the pre-fix code (Expected "C:\Users\lukej\.codex", Received "~/.codex") and passes after the fix (4/4).
• Full-suite baseline diff (clean main vs this branch, per-test timings stripped): 168 pre-existing Windows failures on both sides, zero added, zero removed. The new suite adds four passing tests.

Related

Same cross-platform path class as prior Windows fixes in this area: #398 (sanitize colons in skill/agent names for Windows), #226 (Windows NTFS colons), and issues #366 / #48 / #49 (colon-in-path ENOENT on Windows). Windows is a supported target with a history of exactly these Unix-invisible path bugs.