feat(deepseek api): add balance query and API key management

Add pj deepseek command to query account balance and
pj deepseek setkey to store API key in local cache.

Also extract Python launcher into its own module (pj_python.nu)
and add common aliases (g, c, tree, myip, ports, df, reload, edit).

nushell/modules/pj_python.nu

@@ -0,0 +1,10 @@
+# Python launcher: prefer `py` (Windows launcher), fallback to `python3`
+export def py [...rest: string] {
+    if (which ^py | is-not-empty) {
+        ^py ...$rest
+    } else if (which ^python3 | is-not-empty) {
+        ^python3 ...$rest
+    } else {
+        print "Error: Python is not installed or could not be found."
+    }
+}