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>

Makefile

@@ -15,6 +15,7 @@ install:
 	install -Dm755 packaging/enodia-sentinel.wrapper $(DESTDIR)$(BINDIR)/enodia-sentinel
 	install -Dm755 src/sentinel-redteam $(DESTDIR)$(BINDIR)/sentinel-redteam
 	install -Dm644 systemd/enodia-sentinel.service $(DESTDIR)$(SYSTEMDDIR)/enodia-sentinel.service
+	install -Dm644 systemd/enodia-sentinel-web.service $(DESTDIR)$(SYSTEMDDIR)/enodia-sentinel-web.service
 	@if [ ! -e "$(DESTDIR)$(CONFDIR)/enodia-sentinel.toml" ]; then \
 		install -Dm644 config/enodia-sentinel.toml $(DESTDIR)$(CONFDIR)/enodia-sentinel.toml; \
 		echo "Installed default config at $(CONFDIR)/enodia-sentinel.toml"; \
@@ -30,6 +31,7 @@ uninstall:
 	rm -f $(DESTDIR)$(BINDIR)/enodia-sentinel
 	rm -f $(DESTDIR)$(BINDIR)/sentinel-redteam
 	rm -f $(DESTDIR)$(SYSTEMDDIR)/enodia-sentinel.service
+	rm -f $(DESTDIR)$(SYSTEMDDIR)/enodia-sentinel-web.service
 	rm -f $(DESTDIR)$(CONFDIR)/enodia-sentinel.toml.new
 	@echo "Uninstalled. Config and logs preserved."
 
@@ -56,6 +58,9 @@ check:
 baseline:
 	python3 -m enodia_sentinel.cli baseline
 
+web:
+	python3 -m enodia_sentinel.cli web
+
 drill:
 	./src/sentinel-redteam