fix temporal-dead-zone on PKGX_MIN_VERSION

The previous commit placed `const PKGX_MIN_VERSION = new SemVer("2.4.0")`
above pkgx_meets_minimum() near line ~540, but the top-level dispatch
block (parsedArgs switch at lines 60–126) calls install() → get_pkgx() →
pkgx_meets_minimum() at module-init time, which is BEFORE execution
reaches line 540. `const` declarations are hoisted in name only (TDZ),
unlike `function` declarations whose bodies are hoisted — so the
reference threw `Cannot access 'PKGX_MIN_VERSION' before initialization`
at runtime, causing every `pkgm install` to fail silently with exit 1.

Neither `deno fmt`, `deno lint`, nor `deno check` detect this — it's a
module-init ordering issue invisible to static analysis. Pushed CI on
#86 caught it via the existing `./pkgm.ts i git` test.

Move the constant up to module-scope right after the `hydrate` import,
above any function that's reachable from top-level code.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: tannevaled

pkgm.ts

@@ -13,6 +13,13 @@ import { ensureDir, existsSync, walk } from "jsr:@std/fs@^1";
 import { parseArgs } from "jsr:@std/cli@^1";
 const { hydrate } = plumbing;
 
+// Module-scope SemVer literal: must be defined before any function that
+// reads it can be called from top-level code below. `const` declarations
+// are hoisted in name only (TDZ), so placing this further down the file
+// triggered "Cannot access 'PKGX_MIN_VERSION' before initialization" once
+// install()/get_pkgx() ran at module-init time.
+const PKGX_MIN_VERSION = new SemVer("2.4.0");
+
 function standardPath() {
   let path = "/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin";
 
@@ -535,8 +542,6 @@ function symlink_with_overwrite(src: string, dst: string) {
   Deno.symlinkSync(src, dst);
 }
 
-const PKGX_MIN_VERSION = new SemVer("2.4.0");
-
 function pkgx_meets_minimum(path: string): boolean {
   try {
     const out = new Deno.Command(path, { args: ["--version"] }).outputSync();