Add configurable grid branding

docs/protocol-notes.md

@@ -95,6 +95,7 @@ This is a behavior guide for packet semantics beyond raw schemas.
   - `permissions`
   - `policy` (`usernameMinLength`, `usernameMaxLength`, `passwordMinLength`, `passwordMaxLength`)
 - `auth_required.authPolicy`: server auth limits advertised before login/register submit.
+- `auth_required.gridName` / `auth_required.welcomeMessage`: server-owned pre-login branding values.
 - `auth_result.authPolicy`: server auth limits echoed on auth success/failure responses.
 - `auth_result.sessionToken` is used by the client to call the instance-scoped HTTP endpoint `GET <base_path>auth/session/set` (`Authorization: Bearer <sessionToken>`, `X-Chgrid-Auth-Client: 1`) so the server can issue an instance-scoped `HttpOnly` session cookie.
 - `welcome.worldConfig.gridSize`: server-authoritative grid size used by clients for bounds/drawing.
@@ -104,6 +105,8 @@ This is a behavior guide for packet semantics beyond raw schemas.
 - `welcome.serverInfo`: server process identity/version metadata:
   - `instanceId`: unique id generated at server startup
   - `version`: server package version (or `unknown` fallback)
+  - `gridName`: server-owned user-facing grid name
+  - `welcomeMessage`: server-owned pre-login welcome string
 - `welcome.uiDefinitions`: server-provided item UI definitions:
   - `itemTypeOrder`: add-item menu order
   - `itemTypes[].tooltip`: item-level tooltip/help text

docs/runtime-flow.md

@@ -7,6 +7,7 @@
 3. Client connects signaling websocket from the configured app origin.
 4. Server accepts the socket only on the configured instance websocket path and when the browser `Origin` matches `CHGRID_HOST_ORIGIN`, then attempts cookie-based session resume from the instance-scoped websocket handshake cookie.
 5. If resume does not authenticate, server sends `auth_required`.
+   - includes `gridName` and `welcomeMessage` for pre-login branding.
    - includes `authPolicy` limits for username/password.
 6. Client sends `auth_login` or `auth_register` (or explicit `auth_resume` if provided by caller).
 7. Server sends `auth_result`.
@@ -19,7 +20,7 @@
    - applies `welcome.worldConfig.movementTickMs` as movement pacing guidance
    - applies `welcome.worldConfig.movementMaxStepsPerTick` for movement-rate parity
   - uses `welcome.player` as authoritative starting position (restored from server-side account state when available)
-   - records `welcome.serverInfo` (`instanceId`, `version`) for restart detection
+   - records `welcome.serverInfo` (`instanceId`, `version`, `gridName`, `welcomeMessage`) for restart detection and client branding
    - if `welcome.serverInfo.version` differs from running client version, auto-reloads the page
    - applies `welcome.uiDefinitions` for item menus/properties/options, server-backed command metadata, item-management metadata, and admin menu labels/order
    - sends initial `update_position` echo from server-assigned starting tile