feat(auth): add Discord OAuth sign-in and user timezones

Add persistent user and session storage, protected profile requests, and React sign-in controls. Capture and preserve each user's timezone, and load development and production configuration before migrations and server startup.

.env.example

@@ -1,2 +1,12 @@
+# Optional shared defaults. Values in the selected environment file override these.
 DATABASE_PATH=./data/minabot.sqlite
 PORT=3000
+
+# Discord Developer Portal > OAuth2. Register both redirect URIs:
+# http://127.0.0.1:3000/api/auth/discord/callback
+# https://YOUR_PRODUCTION_HOST/api/auth/discord/callback
+# Credentials may be shared here or set separately in each environment file.
+DISCORD_CLIENT_ID=
+DISCORD_CLIENT_SECRET=
+# Generate once: openssl rand -hex 32 (at least 32 characters required)
+AUTH_COOKIE_SECRET=