Implement wisp: async encrypted single-retrieval file drop

Client-side libsodium encryption with the key in the URL fragment, an
Express/SQLite server holding ciphertext until a confirm-token round trip
proves successful decrypt (avoiding the delete-on-first-byte race), TTL
sweep for unclaimed drops, and a password-gated upload UI styled to match
flit. Dockerized to match the project family's conventions, with a named
volume so the DB/blobs survive redeploys, and a Gitea Actions workflow to
build and push the image.

client/package.json

@@ -0,0 +1,18 @@
+{
+  "name": "wisp-client",
+  "private": true,
+  "license": "MIT",
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "tsc -b && vite build"
+  },
+  "dependencies": {
+    "libsodium-wrappers": "^0.8.4"
+  },
+  "devDependencies": {
+    "@types/libsodium-wrappers": "^0.7.14",
+    "typescript": "^5.6.2",
+    "vite": "^5.4.8"
+  }
+}