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/templates/triggershell.yml

@@ -0,0 +1,35 @@
+# TriggerShell configuration.
+# Full reference: https://dev.pivoine.art/valknar/triggershell.git (see docs/CONFIG_REFERENCE.md)
+
+server:
+  host: 127.0.0.1
+  port: __PORT__
+
+auth:
+  enabled: __AUTH_ENABLED__
+  # Must be >= 32 characters if auth is enabled. Kept out of this file - `triggershell init`
+  # generated one into .env (TRIGGERSHELL_SESSION_SECRET) alongside this config.
+  sessionSecret: "${TRIGGERSHELL_SESSION_SECRET}"
+  sessionTtlHours: 12
+  users: []
+  # Add a user with: triggershell users add <username>
+  tokens: []
+  # Add an API token with: triggershell users add-token <name>
+
+database:
+  path: .triggershell/triggershell.db
+
+logs:
+  dir: .triggershell/logs
+  retentionDays: 30
+
+scripts: []
+# Add scripts like:
+# scripts:
+#   - id: hello-world
+#     name: Hello World
+#     description: A minimal example script.
+#     command: echo
+#     args: ["Hello, TriggerShell!"]
+#     timeoutSeconds: 60
+#     variables: []