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/playground.js

@@ -4,7 +4,7 @@
 //   video → `cortiq animate` over a local text-to-video .cmf (MiniMax-H3)
 // Media results are decoded in the browser (PPM → canvas, MJPEG AVI → canvas
 // player synced to the wav) — the same no-ffmpeg stance as the engine itself.
-import { h, mount, toast, money, ms } from "../ui.js";
+import { h, mount, toast, money, moneyEl, ms } from "../ui.js";
 import { t } from "../i18n.js";
 import { api, testStream, mediaFileUrl, mediaFileBytes } from "../api.js";
 import { appState } from "../app.js";
@@ -218,7 +218,7 @@ export async function renderPlayground() {
       kv(t("pg.tokens"), haveUsage ? `${r.usage_estimated ? "≈ " : ""}${u.prompt_tokens ?? 0} / ${u.completion_tokens ?? 0}` : "—"),
       kv(t("pg.tokSpeed"), tokS != null ? tokS + " tok/s" : "—"),
       kv(t("pg.ttft"), r.ttft_ms != null ? ms(r.ttft_ms) : "—"),
-      kv(t("pg.cost"), money(c.cost_usd)),
+      kv(t("pg.cost"), moneyEl(c.cost_usd)),
       kv(t("pg.latency"), ms(r.latency_ms)),
       kv(t("pg.failover"), c.failover ? "yes" : "no")
     );