fix: use SemVer for pkgx version comparison

`parseFloat("2.10")` evaluates to `2.1`, causing pkgm to silently
reject pkgx 2.10.x as below the minimum version (2.4). Use the
already-imported SemVer class for correct version comparison.

Fixes: pkgm install/uninstall/shim silently fail with exit code 1
when pkgx >= 2.10.0 is installed.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: devmgn

pkgm.ts

@@ -518,8 +518,8 @@ function get_pkgx() {
     if (existsSync(pkgx)) {
       const out = new Deno.Command(pkgx, { args: ["--version"] }).outputSync();
       const stdout = new TextDecoder().decode(out.stdout);
-      const match = stdout.match(/^pkgx (\d+.\d+)/);
-      if (!match || parseFloat(match[1]) < 2.4) {
+      const match = stdout.match(/^pkgx (\d+\.\d+\.\d+)/);
+      if (!match || new SemVer(match[1]).lt(new SemVer("2.4.0"))) {
         Deno.exit(1);
       }
       return pkgx;