Remove multi-tenant company_id scoping from entire codebase

Drop company_id column from all 22 domain tables via migration.
Remove companyId from JWT payload, auth plugins, all service method
signatures (~215 occurrences), all route handlers (~105 occurrences),
test runner, test suites, and frontend auth store/types.

The company table stays as store settings (name, timezone). Tenant
isolation in a SaaS deployment would be at the database level (one
DB per customer) not the application level.

All 107 API tests pass. Zero TSC errors across all packages.

packages/backend/src/plugins/auth.ts

@@ -6,17 +6,16 @@ import { RbacService } from '../services/rbac.service.js'
 
 declare module 'fastify' {
   interface FastifyRequest {
-    companyId: string
     locationId: string
-    user: { id: string; companyId: string; role: string }
+    user: { id: string; role: string }
     permissions: Set<string>
   }
 }
 
 declare module '@fastify/jwt' {
   interface FastifyJWT {
-    payload: { id: string; companyId: string; role: string }
-    user: { id: string; companyId: string; role: string }
+    payload: { id: string; role: string }
+    user: { id: string; role: string }
   }
 }
 
@@ -61,10 +60,7 @@ export const authPlugin = fp(async (app) => {
     sign: { expiresIn: '24h' },
   })
 
-  // Set companyId from header on all requests (for unauthenticated routes like register/login).
-  // Authenticated routes override this with the JWT payload via the authenticate decorator.
   app.addHook('onRequest', async (request) => {
-    request.companyId = (request.headers['x-company-id'] as string) ?? ''
     request.locationId = (request.headers['x-location-id'] as string) ?? ''
     request.permissions = new Set()
   })
@@ -72,7 +68,6 @@ export const authPlugin = fp(async (app) => {
   app.decorate('authenticate', async function (request: any, reply: any) {
     try {
       await request.jwtVerify()
-      request.companyId = request.user.companyId
 
       // Check if user account is active
       const [dbUser] = await app.db