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>

.gitignore

@@ -1,16 +1,4 @@
-# Python
-__pycache__/
-*.py[cod]
-*.egg-info/
-.eggs/
-build/
-dist/
-.venv/
-venv/
-.pytest_cache/
-.ruff_cache/
-
-# Runtime data (created by `triggershell start/dev` in whatever directory the config lives in)
+# Runtime data (created by `triggershell start` in whatever directory the config lives in)
 .triggershell/
 
 # Secrets loaded by `triggershell` via ${VAR} interpolation - never commit these