Add standalone browser mode: no daemon required

BrowserAdapter speaks yaw/2.1 signaling + WebRTC protocol entirely in
the browser (libsodium-wrappers for Ed25519/X25519). Identity stored in
localStorage; peers connect via any waste/yaw2 anchor.

When served from a non-localhost origin the app defaults to browser
mode. On localhost the daemon adapter is tried first with a one-click
switch to browser mode. config.js (gitignored, served by anchor) lets
the host pre-inject signalURL and other defaults.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

web/package-lock.json

@@ -8,6 +8,7 @@
       "name": "web",
       "version": "0.0.0",
       "dependencies": {
+        "libsodium-wrappers": "^0.8.4",
         "react": "^19.2.6",
         "react-dom": "^19.2.6",
         "zustand": "^5.0.14"
@@ -1883,6 +1884,21 @@
         "node": ">= 0.8.0"
       }
     },
+    "node_modules/libsodium": {
+      "version": "0.8.4",
+      "resolved": "https://registry.npmjs.org/libsodium/-/libsodium-0.8.4.tgz",
+      "integrity": "sha512-lMcYaRi0zcs7tarATsQUYC7rstliIXZuoq0c6zXSgNtSNtdvBgkSegjWhpMJAXzKX3SUSwIp7+zEsob+j3LuRw==",
+      "license": "ISC"
+    },
+    "node_modules/libsodium-wrappers": {
+      "version": "0.8.4",
+      "resolved": "https://registry.npmjs.org/libsodium-wrappers/-/libsodium-wrappers-0.8.4.tgz",
+      "integrity": "sha512-mu8aAWucZjTB5O/BtGXtW4e1agy7uHxNYG7zPthmmD1jU43LCDmSWZLN4JhflbdPXj3yDO4lxM1O9hLDgIOXDw==",
+      "license": "ISC",
+      "dependencies": {
+        "libsodium": "^0.8.0"
+      }
+    },
     "node_modules/lightningcss": {
       "version": "1.32.0",
       "resolved": "https://registry.npmjs.org/lightningcss/-/lightningcss-1.32.0.tgz",