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>

docs/CONFIG_REFERENCE.md

@@ -11,7 +11,8 @@ secrets referenced via `${VAR}` don't have to be committed alongside the config.
 init` scaffolds both files together.
 
 The canonical schema is the Zod schema at `app/src/lib/config/schema.ts` — this document mirrors
-it. `triggershell validate` runs the Python pre-flight checks below, then that full schema.
+it. `triggershell validate` loads and validates the config directly against the schema below (no
+separate pre-flight step).
 
 ## `server`