Add ESLint + Prettier + EditorConfig tooling at repo root

v1.0 Phase 1.1 — repo-wide lint/format baseline.

- eslint.config.mjs (flat config) lints server, client, shared
- .prettierrc.json, .prettierignore, .editorconfig, .nvmrc
- Root package.json holds shared devDeps; per-package scripts keep
  their typecheck + test runners
- Fix 7 lint issues surfaced by the baseline run:
  - TicketDetail.tsx: replace ternary-with-side-effects with if/else
  - admin/Users.tsx: escape apostrophe in JSX
  - errorHandler.ts: typed err as unknown with ErrorLike refinement
  - users.ts: Prisma.UserUpdateInput instead of Record<string, any>
  - seed.ts: drop unused goddard binding
- Run prettier across tracked sources for a clean formatting baseline

client/src/main.tsx

@@ -1,10 +1,10 @@
-import { StrictMode } from 'react'
-import { createRoot } from 'react-dom/client'
-import './index.css'
-import App from './App'
+import { StrictMode } from 'react';
+import { createRoot } from 'react-dom/client';
+import './index.css';
+import App from './App';
 
 createRoot(document.getElementById('root')!).render(
   <StrictMode>
     <App />
-  </StrictMode>
-)
+  </StrictMode>,
+);