Add read-only web dashboard and phone push notifications

Both zero-dependency (stdlib http.server + urllib), consistent with the
project's no-dependency-tree stance for a security daemon.

Web dashboard (enodia_sentinel/web.py + static/dashboard.html):
- read-only JSON API over the log dir: /api/status, /api/alerts,
  /api/alerts/<id>, /api/events
- bearer-token auth (constant-time; header or ?token=), required on non-
  loopback binds, auto-generated + persisted (0600) when unset
- binds the host's Tailscale IP by default (auto-detected), reachable from the
  tailnet but not the LAN/internet
- self-contained dark SPA: severity cards, live alert list, full snapshot
  viewer; 10s auto-refresh
- path-traversal-safe alert lookup; `enodia-sentinel web` subcommand; daemon
  now writes a pidfile so the dashboard can show live status
- hardened enodia-sentinel-web.service (read-only, no caps)

Phone push (enodia_sentinel/notify/):
- pluggable backends — ntfy, Pushover, generic webhook — each separating a pure
  build() (unit-tested, no network) from send()
- a backend turns on when its config keys are set; pushes gated by
  notify_min_severity; severity → per-service priority/tags
- fired from snapshot.capture on worker threads, errors swallowed
- desktop notify-send retained

Tests: +16 (9 web incl. a real-server 401/200 auth test, 7 notify request-build
cases). 55/55 pass. Live end-to-end verified: daemon → alert → API → page.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

packaging/PKGBUILD

@@ -1,6 +1,6 @@
 # Maintainer: Enodia
 pkgname=enodia-sentinel
-pkgver=0.3.0
+pkgver=0.4.0
 pkgrel=1
 pkgdesc="Host intrusion-detection daemon — signature-based detection of reverse shells, LD_PRELOAD rootkits, fileless malware, and persistence tampering"
 arch=('any')
@@ -22,6 +22,7 @@ package() {
     install -Dm755 packaging/enodia-sentinel.wrapper "$pkgdir/usr/bin/enodia-sentinel"
     install -Dm755 src/sentinel-redteam "$pkgdir/usr/bin/sentinel-redteam"
     install -Dm644 systemd/enodia-sentinel.service "$pkgdir/usr/lib/systemd/system/enodia-sentinel.service"
+    install -Dm644 systemd/enodia-sentinel-web.service "$pkgdir/usr/lib/systemd/system/enodia-sentinel-web.service"
     install -Dm644 config/enodia-sentinel.toml "$pkgdir/etc/enodia-sentinel.toml"
     install -Dm644 LICENSE "$pkgdir/usr/share/licenses/$pkgname/LICENSE"
     install -dm750 "$pkgdir/var/log/enodia-sentinel"