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>

cli/src/app.rs

@@ -721,6 +721,7 @@ fn provider_config(preset: &crate::models::Preset, base_url: &str, key: &str) ->
         enabled: true,
         max_concurrency: None,
         monthly_budget: None,
+        plan_limit: None,
         admin_key: String::new(),
     }
 }