feat: Migrate Arbiter and Modpack Version Checker to monorepo

WHAT WAS DONE:
- Migrated Arbiter (discord-oauth-arbiter) code to services/arbiter/
- Migrated Modpack Version Checker code to services/modpack-version-checker/
- Created .env.example for Arbiter with all required environment variables
- Moved systemd service file to services/arbiter/deploy/
- Organized directory structure per Gemini monorepo recommendations

WHY:
- Consolidate all service code in one repository
- Prepare for Gemini code review (Panel v1.12 compatibility check)
- Enable service-prefixed Git tagging (arbiter-v2.1.0, modpack-v1.0.0)
- Support npm workspaces for shared dependencies

SERVICES MIGRATED:
1. Arbiter (Discord OAuth bot) - Originally written by Gemini + Claude
   - Full source code from ops-manual docs/implementation/
   - Created comprehensive .env.example
   - Ready for Panel v1.12 compatibility verification

2. Modpack Version Checker (Python CLI tool)
   - Full source code from ops-manual docs/tasks/
   - Written for Panel v1.11, needs Gemini review for v1.12
   - Never had code review before

STILL TODO:
- Whitelist Manager - Pull from Billing VPS (38.68.14.188)
  - Currently deployed and running
  - Needs Panel v1.12 API compatibility fix (Task #86)
  - Requires SSH access to pull code

NEXT STEPS:
- Gemini code review for Panel v1.12 API compatibility
- Create package.json for each service
- Test npm workspaces integration
- Deploy after verification

FILES:
- services/arbiter/ (25 new files, full application)
- services/modpack-version-checker/ (21 new files, full application)

Signed-off-by: The Golden Chronicler <claude@firefrostgaming.com>

services/modpack-version-checker/src/modpack_checker/config.py

@@ -0,0 +1,46 @@
+"""Configuration management for Modpack Version Checker."""
+
+from __future__ import annotations
+
+import json
+from pathlib import Path
+from typing import Optional
+
+from pydantic import BaseModel, Field
+
+CONFIG_DIR = Path.home() / ".config" / "modpack-checker"
+CONFIG_FILE = CONFIG_DIR / "config.json"
+DEFAULT_DB_PATH = str(CONFIG_DIR / "modpacks.db")
+
+
+class Config(BaseModel):
+    """Application configuration, persisted to ~/.config/modpack-checker/config.json."""
+
+    curseforge_api_key: str = ""
+    discord_webhook_url: Optional[str] = None
+    database_path: str = DEFAULT_DB_PATH
+    check_interval_hours: int = Field(default=6, ge=1, le=168)
+    notification_on_update: bool = True
+
+    @classmethod
+    def load(cls) -> "Config":
+        """Load configuration from disk, returning defaults if not present."""
+        if CONFIG_FILE.exists():
+            try:
+                with open(CONFIG_FILE) as f:
+                    data = json.load(f)
+                return cls(**data)
+            except (json.JSONDecodeError, ValueError):
+                # Corrupted config — fall back to defaults silently
+                return cls()
+        return cls()
+
+    def save(self) -> None:
+        """Persist configuration to disk."""
+        CONFIG_DIR.mkdir(parents=True, exist_ok=True)
+        with open(CONFIG_FILE, "w") as f:
+            json.dump(self.model_dump(), f, indent=2)
+
+    def is_configured(self) -> bool:
+        """Return True if the minimum required config (API key) is present."""
+        return bool(self.curseforge_api_key)