feat(frontend): v2 rewrite — Vite + React + TS readonly SPA

Replaces the v1 CRA app (which targeted the obsolete Python Dialectic
backend) with a fresh Vite + React 18 + TypeScript scaffold that talks
to Dialectic.Backend Go v2.

Pages (all readonly — propose/signup/post are agent-only by design):
  - /                       TopicList — filter by status, paginated
  - /topics/:id             TopicDetail — meta + camps + transcript
                            (polling every 8s)
  - /topics/:id/verdict     Verdict permalink (shareable)
  - /agents/:id             AgentActivity — admin diagnostics card

Stack:
  - Vite 5 + React 18 + react-router-dom 6
  - Pure ESM, NodeNext-style imports, .tsx
  - Style: ~/STYLE.md tokens (IBM Plex Mono + Major Mono Display +
    --acid #d8ff3e on --ink #080a0d, with subtle blueprint grid wash)

Auth:
  - v1 dev-bypass only — VITE_OIDC_DEV_BYPASS auto-attaches
    x-dev-bypass header. Real Keycloak OIDC redirect ships as v2.
  - Admin endpoints (x-dialectic-admin-key) prompt on first visit
    and store key in localStorage. Never baked into bundle. Never
    sent to non-admin endpoints.

Backend pairing:
  - Dialectic.Backend@0b16b52 adds GET /api/admin/agents/{id} for the
    AgentActivity page. AgentActivity calls it via the admin-key
    branch in api.ts.

Deploy:
  - Multi-stage Dockerfile (node:22-alpine build → nginx:1.27-alpine
    serve). nginx.conf reverse-proxies /api/ → dialectic-backend:8090
    so the browser sees one origin (no CORS).

Reuses the existing hzhang/Dialectic.Frontend repo — old CRA contents
nuked in this commit. History preserved on master.

vite.config.js

@@ -0,0 +1,21 @@
+import { defineConfig } from 'vite';
+import react from '@vitejs/plugin-react';
+// Dev server proxies /api → the dialectic-backend so the SPA can run
+// without CORS knobs at dev time. In prod the SPA + backend sit behind
+// the same hostname (nginx rewrites /api/ → backend container).
+export default defineConfig({
+    plugins: [react()],
+    server: {
+        port: 5173,
+        proxy: {
+            '/api': {
+                target: process.env.VITE_DIALECTIC_BACKEND ?? 'http://localhost:8090',
+                changeOrigin: false,
+            },
+        },
+    },
+    build: {
+        outDir: 'dist',
+        sourcemap: true,
+    },
+});