Statistics: traffic, drops, devices and connections over time

internal/stats samples every minute what the kernel already counts: the
interfaces' counters (per zone too), Housecarl's table (hits per rule,
built-in and policy; drops by chain; quotas; per-device sets), the
connection tracking table, and housecarld's and the host's memory, CPU
and load. Logged drops feed top lists of sources and what they tried.
Aggregates go to a database of their own (stats.db; per minute 7 days,
per hour 90 days, per day 2 years), with the store and queries from
Jarl's.

Traffic per inside device is a setting (stats_per_device): counting sets
stats_up/down_v4/v6 and rules at the top of the forward chain, IPv6 per
/64, carried across reloads. Set names starting with meter_, conn_,
quota_ or stats_ are reserved (set_name_reserved).

GET /stats/{status,summary,timeline,top,hits,heatmap}, hc stats, a
Statistics page with Jarl's charts, two charts on the dashboard, and a
conntrack_full warning. e2e: 188 checks.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

internal/web/static/assets/app.js

@@ -6,6 +6,7 @@ import * as changes from "./pages/changes.js";
 import * as connections from "./pages/connections.js";
 import * as tracePage from "./pages/trace.js";
 import * as matrixPage from "./pages/matrix.js";
+import * as statsPage from "./pages/stats.js";
 import * as dashboard from "./pages/dashboard.js";
 import * as rules from "./pages/rules.js";
 import * as nat from "./pages/nat.js";
@@ -32,6 +33,7 @@ const routes = [
   { pattern: /^log$/, page: log, nav: "log" },
   { pattern: /^connections$/, page: connections, nav: "connections" },
   { pattern: /^trace$/, page: tracePage, nav: "trace" },
+  { pattern: /^stats$/, page: statsPage, nav: "stats" },
   { pattern: /^settings$/, page: settings, nav: "settings" },
   { pattern: /^import$/, page: importPage, nav: "import" },
   { pattern: /^changes$/, page: changes, nav: "changes" },
@@ -55,6 +57,7 @@ const navItems = [
     ["services", "#/services", "Services", "config"],
   ] },
   { menu: "Traffic", items: [
+    ["stats", "#/stats", "Statistics", "log"],
     ["log", "#/log", "Log", "log"],
     ["connections", "#/connections", "Connections", "log"],
     ["trace", "#/trace", "Trace", "log"],