Replace the Python CLI with a Node CLI, add a systemd service command

The app is already 100% Node, so the Python launcher was pure overhead - it
existed mainly to bootstrap Node, which is circular. The CLI is now merged
into app/ (the single published npm package): `triggershell start` validates
the config and imports server.ts directly in-process, so server.ts's own
SIGTERM/SIGINT handling just works with no signal-relay/child-process layer
needed. `dev` is dropped from the public CLI (contributors use `pnpm --dir
app dev` directly); there's no `build` command either, since the package
ships a prebuilt `.next` via a `prepack` hook. Adds `triggershell service
install|uninstall|status` for running as a per-user or system systemd unit.

Also fixes two bugs found while wiring this up: server.ts resolved `.next`
relative to `process.cwd()`, which broke once the CLI could run from a
directory other than the app itself; and an explicitly-`files`-listed
package directory bypasses .npmignore for its subpaths, so `.next/cache`
was inflating the npm tarball to ~670MB (now stripped in `prepack`, ~7MB).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

app/README.md

@@ -1,8 +1,9 @@
 # TriggerShell web app
 
-This is the Next.js app that TriggerShell's Python CLI (`triggershell dev` / `triggershell start`)
-launches — it's not meant to be run standalone with `next dev`/`next start` since it needs a
-custom server (`server.ts`) for the WebSocket endpoint.
+This directory is both the Next.js app and the home of the `triggershell` CLI (`bin/triggershell.js`
+→ `src/cli`) that launches it — together they're published as one npm package. The app is still not
+meant to be run standalone with `next dev`/`next start`, since it needs a custom server (`server.ts`)
+for the WebSocket endpoint; use the CLI (`triggershell start`) or the `pnpm` scripts below instead.
 
 See the [repo root README](../README.md) for how to run TriggerShell end-to-end, and
 [`../docs/ARCHITECTURE.md`](../docs/ARCHITECTURE.md) for how this app is put together.
@@ -12,5 +13,9 @@ pnpm install
 pnpm dev          # tsx watch server.ts - reads TRIGGERSHELL_CONFIG_PATH from the environment
 pnpm lint
 pnpm typecheck
+pnpm test         # CLI unit tests (src/cli/**/*.test.ts)
 pnpm db:studio    # browse the SQLite database
 ```
+
+Note: this is the contributor workflow for developing TriggerShell itself. End users install and
+run the published `triggershell` CLI instead (see the root README).