Fix achievement icons in launcher, allow opening OAuth URLs, live map docs

- Shared achievement icon catalogue; launcher resolves icon/background/border ids
- Tauri opener capability now allows http(s) URLs (fixes Discord sign-in)
- Rewrite live map docs, admin guide progression section

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01DjMbLQujBHunCCu5GpsHaT

.env.example

@@ -10,3 +10,7 @@ RUST_LOG=info
 PUBLIC_URL=
 # Comma-separated IPs of your reverse proxies; blank means forwarded IP headers are ignored.
 SCOPENET_TRUSTED_PROXIES=
+
+# Live Map: optional static Vantage Linux release to bundle, and memory for the panel.
+VANTAGE_URL=
+PANEL_MEMORY=256M