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>

server/src/app.rs

@@ -144,6 +144,11 @@ impl App {
                 Ok(n) => tracing::info!("moved {n} images of older chats to the image store"),
                 Err(e) => tracing::warn!("moving images to the image store: {e:#}"),
             }
+            match crate::budget::value_plan_requests(&self) {
+                Ok(0) => {}
+                Ok(n) => tracing::info!("valued {n} plan requests (opencode Go) at list prices"),
+                Err(e) => tracing::warn!("valuing plan requests: {e:#}"),
+            }
             match crate::images::backfill_copies(&self) {
                 Ok(0) => {}
                 Ok(n) => tracing::info!("kept copies of {n} generated images in the image store"),