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/css/styles.css

@@ -585,6 +585,9 @@ body.modal-open { overflow: hidden; }
 /* Featured gallery: the list grows as new models are published, so give it more
    room than the search grid before it starts scrolling. */
 .featured-section .hf-grid { max-height: min(62vh, 760px); }
+/* Money: 4 decimals, last two de-emphasized */
+.money-tail { font-size: .72em; opacity: .75; margin-left: 1px; }
+
 /* Benchmark view */
 @keyframes bm-in { from { opacity: 0; transform: translateY(-3px); } to { opacity: 1; transform: none; } }
 tbody tr:last-child { animation: bm-in .25s ease; }