Restyle server browser UI; hide overlay on join

Restyles the server browser to match main-menu/settings (Futura PT Demibold, amber/green palette, yellow selection bars, shared panel chrome), removes SVG border strips, and tweaks modal width/layout. Adds JS + C++ coordination so the custom main-menu overlay hides when a server join begins (C++ invokes onSessionLoading and calls HideMainMenu; CompleteJoinFailure restores the menu/browser). Controller glyph tint now derives from --co-amber. Updates changelog and dev-log; includes compiled Vault109 script update.

docs/dev-log.md

@@ -9,6 +9,36 @@ failed experiments, successful tests, and next steps.
 
 ---
 
+## 2026-07-07 - Fix: Hide Main Menu Overlay During Server Join Load
+
+### Summary
+When joining a server from the custom main menu, the PrismaUI overlay (left nav, server browser, settings) stayed visible and interactive while the vanilla loading screen appeared underneath. The overlay now hides as soon as server validation succeeds and game load begins; failed joins restore the main menu and browser with the error overlay.
+
+### Files Changed
+- `plugin/src/F4TServerBrowserBridge.cpp`
+- `ui/views/CommonwealthOnline/main-menu/script.js`
+- `ui/views/CommonwealthOnline/main-menu/styles.css`
+- `changelog.md`
+- `docs/dev-log.md`
+
+### Details
+- `JoinServerEntry` invokes `onSessionLoading` in JS, then calls `HideMainMenu()` after the `joinLoading` / "Loading game..." event.
+- `CompleteJoinFailure` restores the main menu and browser before dispatching `joinFailed` so the error overlay can display.
+- JS `onSessionLoading` collapses open sub-panels and applies `is-session-loading` (non-interactive) as a same-frame fallback before C++ hides the view.
+
+### Testing
+- Not run locally (requires Fallout 4 + built plugin).
+- Expected: connect from main menu → overlay disappears → loading screen visible and unobstructed.
+- Expected on failure: overlay returns with join error message in browser.
+
+### Known Issues
+- None currently known.
+
+### Next Steps
+- In-game verification with two clients after deploy.
+
+---
+
 ## 2026-07-07 - Fix: Trampoline Crash on Load (MenuCursor Hook Replaced)
 
 ### Summary