fix(deploy): install frontend prod deps on server after deploy

adapter-node bundles the SvelteKit framework but leaves package.json
`dependencies` (clsx, bits-ui, etc.) external — they must be present in
node_modules on the server at runtime.

- deploy.sh: rsync package.json + pnpm-lock.yaml, run pnpm install --prod
- DEPLOYMENT.md: add pnpm to server setup with explanation

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

docs/DEPLOYMENT.md

@@ -69,10 +69,12 @@ curl -LsSf https://astral.sh/uv/install.sh | UV_INSTALL_DIR=/usr/local/bin sh
 
 Installing to `/usr/local/bin` makes `uv` available system-wide (required for `sudo -u innercontext uv sync`).
 
-### Node.js 24 LTS
+### Node.js 24 LTS + pnpm
 
-The server only needs Node.js to **run** the pre-built frontend bundle.
-`pnpm` is **not** needed on the server — the frontend is always built locally.
+The server needs Node.js to **run** the pre-built frontend bundle, and pnpm to
+**install production runtime dependencies** (`clsx`, `bits-ui`, etc. —
+`adapter-node` bundles the SvelteKit framework but leaves these external).
+The frontend is never **built** on the server.
 
 ```bash
 curl -o- https://raw.githubusercontent.com/nvm-sh/nvm/v0.40.4/install.sh | bash
@@ -88,6 +90,15 @@ Use `--remove-destination` to replace any existing symlink with a real file:
 cp --remove-destination "$(nvm which current)" /usr/local/bin/node
 ```
 
+Install pnpm as a standalone binary — self-contained, no wrapper scripts,
+works system-wide:
+
+```bash
+curl -fsSL "https://github.com/pnpm/pnpm/releases/latest/download/pnpm-linux-x64" \
+  -o /usr/local/bin/pnpm
+chmod 755 /usr/local/bin/pnpm
+```
+
 ### Application user
 
 ```bash