Value opencode Go plan requests; per-duration cache prices; usage under answers

- opencode Go reports plan requests as cost 0 with the usage in allowance;
  ModelConfig::cost values them at the model's list prices (charged amounts
  and free requests stay as reported). Rows booked at 0 are valued once on
  start (idempotent).
- opencode's price list now has per-duration cache prices for some models
  ({"30m": ..., "12h": ...}): the shortest duration is used, also in tiers.
  Saving the provider's models failed with "untagged enum ModelEntry".
- Each answer shows tokens sent/received and the cost of the turn's requests
  (usage.cost filled when messages are saved and loaded).
- The chat title keeps a minimum width in a crowded top bar.

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

web/src/whatsnew.ts

@@ -3,6 +3,10 @@
  * under "unreleased"; scripts/release.sh renames the key to the release version.
  */
 export const WHATS_NEW: Record<string, { en: string[]; de: string[] }> = {
+  unreleased: {
+    en: ["Tokens and cost under every answer; the total cost of chats with opencode Go is shown correctly again"],
+    de: ["Tokens und Kosten unter jeder Antwort; der Gesamtpreis von Chats mit opencode Go stimmt wieder"],
+  },
   "202611-00022": {
     en: ["New theme “Tintenblau” (Settings → General → Theme)"],
     de: ["Neues Theme „Tintenblau“ (Einstellungen → Allgemein → Theme)"],