Add Alerts webapp UI (ticket 020)

New Alerts panel: lists rules with condition summaries and an enabled
toggle, and a condition-type-specific editor (Immediate/Threshold/NewValue/
Ratio) with client-side validation before save, reusing FilterBar's query
input styling for query-based conditions. Adds a test-notification endpoint
(POST /api/settings/alerts/test) so an ntfy topic/server can be verified
without saving a rule first, plus a docs section and help icons matching
ticket 021's pattern.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01XFUNZwCvz3kcod3352ZR2o

webapp/src/App.tsx

@@ -5,6 +5,7 @@ import { LogTimeline, computePresetRange, type TimeRange, type TimeRangePresetId
 import { LogPreview } from './components/LogPreview'
 import { Metrics } from './components/Metrics'
 import { Dashboards } from './components/Dashboards'
+import { Alerts } from './components/Alerts'
 import { fetchLogs, fetchStats, fetchTimeline, type LogEntry, type Stats, type TimelineBucket } from './lib/api'
 import { DocsNavProvider } from './lib/docsNav'
 
@@ -110,6 +111,7 @@ export default function App() {
           <LogPreview logs={logs} />
           <Metrics range={range} />
           <Dashboards range={range} />
+          <Alerts />
         </div>
       </div>
     </DocsNavProvider>