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/bin/triggershell.js

@@ -0,0 +1,5 @@
+#!/usr/bin/env node
+import { register } from "tsx/esm/api";
+
+register();
+await import("../src/cli/index.ts");