fix: honest costs in streams, oracle-sized timeouts, history & log cleanup

Cost showed $0 for every streamed request: the X-Cortiq-Cost-USD header is
written before generation, when the cost cannot be known. The gateway now
ships the final number in a closing SSE event (`cortiq_cost_usd`, alongside
the token estimate when the provider sent no usage), and the console prefers
it over the header. Money renders with 4 decimals, the last two in a smaller
font — $0.0006 stays readable instead of collapsing to $0.

Timeouts, both ends: the router default was 800 ms, silently degrading every
prompt the hosted router escalates to its oracle (~10 s) — now 15 s. Provider
clients had NO timeout at all (a dead OpenRouter host hung requests forever) —
now a 10 s connect timeout, with no overall cap so long generations and
streams are never cut.

Benchmark history: per-run × and a Clear-all button. Logs view: a clear
button backed by DELETE /admin/api/logs.

web/js/views/dashboard.js

@@ -1,5 +1,5 @@
 // Dashboard — KPIs, time-series charts, breakdown, recent requests, health.
-import { h, mount, money, num, ms, pct, timeAgo, toast, confirmDialog } from "../ui.js";
+import { h, mount, money, moneyEl, num, ms, pct, timeAgo, toast, confirmDialog } from "../ui.js";
 import { t } from "../i18n.js";
 import { api } from "../api.js";
 import { lineChart, barList } from "../charts.js";
@@ -161,7 +161,7 @@ export async function renderDashboard() {
         { class: "kpis" },
         kpi(num(tot.requests), t("dash.kpi.requests")),
         kpi(num(tot.total_tokens), t("dash.kpi.tokens")),
-        kpi(money(tot.cost_usd), t("dash.kpi.cost")),
+        kpi(moneyEl(tot.cost_usd), t("dash.kpi.cost")),
         kpi(ms(tot.avg_latency_ms), t("dash.kpi.latency")),
         kpi(pct(tot.success_rate), t("dash.kpi.success")),
         kpi(num(tot.failovers), t("dash.kpi.failovers"))