Fix question counter daily reset, rate-limit timer, and founding member pricing clarity

- chat-widget: session.count now resets on new UTC day (keeps client in sync with server's daily quota reset)
- chat-widget: fix rate-limit timer — wrong element IDs (neuron-demo-msgs → neuron-demo-messages) and wrong class (.neuron-msg-ai → .demo-msg-ai) meant the countdown never updated
- chat-widget: remove btn.disabled=false that immediately re-enabled the send button after rate-limiting
- main.el: add POST /api/admin/reset-rate-limits endpoint (requires NEURON_ADMIN_TOKEN, deletes all demo_rate_limits rows)
- pricing.el: clarify founding member card — software updates are free forever, inference is pay-per-use at founding member rate

src/pricing.el

@@ -51,9 +51,9 @@ fn pricing_pro_features() -> String {
 }
 
 fn pricing_founding_features() -> String {
-    el_li("", el_span("class=\"dash\"", "-") + el_span("", "Neuron Inference (Q3 2026) - founding member rate, priced below the major APIs")) +
+    el_li("", el_span("class=\"dash\"", "-") + el_span("", "Neuron Inference (Q3 2026) - pay-per-use at the founding member rate, below the major APIs")) +
     el_li("", el_span("class=\"dash\"", "-") + el_span("", "Everything in Professional - forever")) +
-    el_li("", el_span("class=\"dash\"", "-") + el_span("", "Never pay again - lifetime updates included")) +
+    el_li("", el_span("class=\"dash\"", "-") + el_span("", "No subscription — software updates are free forever")) +
     el_li("", el_span("class=\"dash\"", "-") + el_span("", "Founding member badge in the app")) +
     el_li("", el_span("class=\"dash\"", "-") + el_span("", "Private founding member community")) +
     el_li("", el_span("class=\"dash\"", "-") + el_span("", "Shape the roadmap - your votes carry more weight")) +
@@ -125,7 +125,7 @@ fn pricing(sold: Int, total: Int) -> String {
             el_span("class=\"pricing-price\"", "$199") +
             el_span("class=\"pricing-cadence\"", "lifetime")
         ) +
-        el_p("class=\"pricing-tagline\"", "Pay once. Everything, forever. Including Neuron Inference when it launches.") +
+        el_p("class=\"pricing-tagline\"", "Pay once for the platform — free software updates, forever. Inference is pay-per-use at your founding member rate.") +
         spots_html +
         el_ul("class=\"pricing-features\"", pricing_founding_features()) +
         el_div("style=\"flex:1\"", "") +