feat(phase-a): remove Neo4j from startup chain, clean auth flow

- Remove NeoUserProvider + NeoInstituteProvider from App.tsx startup chain
- Strip user_db_name/school_db_name from CCUser; add school_id (Phase B wires it to Supabase)
- Remove DatabaseNameService from AuthContext and UserContext
- Remove provisionUser() call from login path; API endpoint preserved for Phase B decision
- Simplify UserContext.resolveProfile: fast-path JWT metadata then background Supabase fetch
- Replace user.user_db_name reads in singlePlayerPage + snapshotService with null-safe guards
- Add useDeviceContext hook (desktop/tablet/phone/iwb, persists to localStorage)

App now loads to dashboard without any Neo4j dependency at startup.
Canvas opens to blank TLDraw state; Phase B rebuilds navigation on Supabase.

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

src/services/auth/registrationService.ts

@@ -6,7 +6,6 @@ import { RegistrationResponse } from '../../services/auth/authService';
 import { storageService, StorageKeys } from './localStorageService';
 import { logger } from '../../debugConfig';
 import { provisionUser } from '../provisioningService';
-import { DatabaseNameService } from '../graph/databaseNameService';
 
 const REGISTRATION_SERVICE = 'registration-service';
 
@@ -87,14 +86,6 @@ export class RegistrationService {
             try {
                 const provisioned = await provisionUser(ccUser.id, provisioningToken);
                 if (provisioned) {
-                    ccUser.user_db_name = provisioned.user_db_name;
-                    if (provisioned.worker_db_name) {
-                        ccUser.school_db_name = provisioned.worker_db_name;
-                    }
-                    DatabaseNameService.rememberDatabaseNames({
-                        userDbName: ccUser.user_db_name,
-                        schoolDbName: ccUser.school_db_name
-                    });
                     logger.info(REGISTRATION_SERVICE, '✅ Provisioning successful', {
                         userId: ccUser.id,
                         userDbName: provisioned.user_db_name,
@@ -110,11 +101,6 @@ export class RegistrationService {
                 });
             }
 
-            DatabaseNameService.rememberDatabaseNames({
-                userDbName: ccUser.user_db_name,
-                schoolDbName: ccUser.school_db_name
-            });
-
             return {
                 user: ccUser,
                 accessToken: authData.session?.access_token || null,