opencode prices and Go limits, settings out of .env

- Fetch prices for opencode (Zen and Go) incl. limits, image input, reasoning,
  long-context tiers and peak-hour/date factors; costs apply them per request
- Record the cost opencode reports per response; track Go allowance in 5h/7d/month
  windows against a provider plan limit (budget table, status overlay)
- Settings → Config file: move values of ${NAME} references into the config
- Examples, presets and forms keep keys in the config instead of .env

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

web/src/styles.css

@@ -3569,3 +3569,37 @@ button.danger-solid {
   border-color: var(--accent);
   color: var(--accent);
 }
+
+.chip.price-extra {
+  margin-left: 4px;
+  font-size: 11px;
+  cursor: help;
+}
+
+.plan-row td {
+  border-top: none;
+  padding-top: 0;
+}
+.plan-usage {
+  display: flex;
+  gap: 16px;
+  flex-wrap: wrap;
+}
+.plan-window {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  font-size: 12px;
+  min-width: 170px;
+}
+.plan-window .budget-bar {
+  flex: 1;
+  min-width: 60px;
+}
+.plan-label {
+  color: var(--muted);
+  white-space: nowrap;
+}
+.plan-pct {
+  font-variant-numeric: tabular-nums;
+}