fix: strip user: prefix from Discord allowed user IDs in onboarding

Users sometimes paste Discord IDs with prefixes like 'user:123456',
'<@123456>', or '<@!123456>' from Discord's UI or third-party tools.
This caused auth failures since the allowlist contained 'user:123' but
the actual user_id from messages was just '123'.

Fixes:
- Added _clean_discord_id() helper in discord.py to strip common prefixes
- Applied sanitization at runtime when parsing DISCORD_ALLOWED_USERS env var
- Applied sanitization in hermes setup and hermes gateway setup input flows
- Handles user:, <@>, and <@!> prefix formats

hermes_cli/gateway.py

@@ -623,6 +623,18 @@ def _setup_standard_platform(platform: dict):
             value = prompt(f"  {var['prompt']}", password=False)
             if value:
                 cleaned = value.replace(" ", "")
+                # For Discord, strip common prefixes (user:123, <@123>, <@!123>)
+                if "DISCORD" in var["name"]:
+                    parts = []
+                    for uid in cleaned.split(","):
+                        uid = uid.strip()
+                        if uid.startswith("<@") and uid.endswith(">"):
+                            uid = uid.lstrip("<@!").rstrip(">")
+                        if uid.lower().startswith("user:"):
+                            uid = uid[5:]
+                        if uid:
+                            parts.append(uid)
+                    cleaned = ",".join(parts)
                 save_env_value(var["name"], cleaned)
                 print_success(f"  Saved — only these users can interact with the bot.")
                 allowed_val_set = cleaned