feat(amneziawg): add a button to randomize obfuscation parameters

Mirrors the existing key-regenerate button next to the private key
field. Client-side randomization matches the ranges/constraints of
GenerateObfuscation20's "default" preset (internal/amneziawg/params.go)
closely enough for a form suggestion — the user can still hand-edit any
field afterward.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

internal/web/translation/en-US.json

@@ -1933,6 +1933,8 @@
         "secondaryDns": "Secondary DNS",
         "externalInterface": "External Interface",
         "externalInterfaceHint": "Host NIC for NAT (PostUp/PostDown). Leave empty to auto-detect.",
+        "obfuscation": "Obfuscation parameters",
+        "regenerateObfuscation": "Regenerate",
         "jc": "Jc (junk packet count)",
         "jmin": "Jmin (junk packet min size)",
         "jmax": "Jmax (junk packet max size)",