feat: initial scaffold of uniweb — unibus web frontend (SPA + gateway)

Extracted from unibus v0.13.0: the chat SPA (web/, React+Mantine, per-user
BIP39 wallet) and the web gateway (cmd/webgw, REST+SSE) that acts as a bus
peer for the browser. Consumes unibus as a Go module via replace => ../unibus,
keeping its own replace fn-registry for the cybersecurity primitives.

go build/vet/test and pnpm build green in the new location.

web/package.json

@@ -0,0 +1,31 @@
+{
+  "name": "unibus-web",
+  "private": true,
+  "version": "0.1.0",
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "tsc -b && vite build",
+    "preview": "vite preview"
+  },
+  "dependencies": {
+    "@mantine/core": "^9.3.0",
+    "@mantine/hooks": "^9.3.0",
+    "@noble/curves": "^2.2.0",
+    "@noble/hashes": "^2.2.0",
+    "@scure/bip39": "^2.2.0",
+    "@tabler/icons-react": "^3.36.0",
+    "react": "^19.2.0",
+    "react-dom": "^19.2.0"
+  },
+  "devDependencies": {
+    "@types/react": "^19.2.0",
+    "@types/react-dom": "^19.2.0",
+    "@vitejs/plugin-react": "^4.3.4",
+    "postcss": "^8.4.49",
+    "postcss-preset-mantine": "^1.17.0",
+    "postcss-simple-vars": "^7.0.1",
+    "typescript": "~5.6.3",
+    "vite": "^6.0.3"
+  }
+}