feat: add charts, world map, and filters to web dashboard

Add Chart.js line/bar charts for attack trends (attempts over time,
hourly pattern), an SVG world map choropleth colored by attack origin
country, and a collapsible filter form (date range, IP, country,
username) that narrows both charts and top-N tables.

New store methods: GetAttemptsOverTime, GetHourlyPattern, GetCountryStats,
and filtered variants of dashboard stats/top-N queries. New JSON API
endpoints at /api/charts/* and an htmx fragment at
/fragments/dashboard-content for filtered table updates.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

README.md

@@ -44,6 +44,7 @@ Key settings:
 - `shell.fake_user` — override username in prompt; empty uses the authenticated user
 - `web.enabled` — enable the web dashboard (default `false`)
 - `web.listen_addr` — web dashboard listen address (default `:8080`)
+  - Dashboard includes Chart.js charts (attempts over time, hourly pattern), an SVG world map choropleth colored by attack origin, and filter controls for date range / IP / country / username
   - Session detail pages at `/sessions/{id}` include terminal replay via xterm.js
 - `web.metrics_enabled` — expose Prometheus metrics at `/metrics` (default `true`)
 - `web.metrics_token` — bearer token to protect `/metrics`; empty means no auth (default empty)