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>

core/src/provider/anthropic.rs

@@ -266,6 +266,7 @@ impl Provider for Anthropic {
                     if let Some(o) = data["usage"]["output_tokens"].as_u64() {
                         usage.output_tokens = o;
                     }
+                    usage.read_reported_cost(&data["usage"]);
                 }
                 "error" => {
                     let msg = data["error"]["message"].as_str().unwrap_or("unknown error");