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>

server/src/runner.rs

@@ -882,6 +882,7 @@ async fn stream_step(
             cost: req.model.cost(usage),
             error,
             user_id: None,
+            allowance: usage.allowance,
         };
 
         if let Err(e) = result {
@@ -967,6 +968,7 @@ fn record_side_usage(app: &App, session: &Session, spec: &str, model: &crate::co
         cost: model.cost(usage),
         error: false,
         user_id: None,
+        allowance: usage.allowance,
     });
 }