Move closure scenarios from YAML to SQLite

[Copilot]

Closure scenarios are now database-backed, and the policy UI supports selecting closures from existing spatial or grid variables. This removes runtime YAML dependencies from closure creation, simulation, polling, and table discovery.

• Closure selection UI

  • Adds Select Existing Variable mode.
  • Populates selectable columns from spatial and grid data.
  • Selects matching second_location_id values and updates the map/TAC table.

• SQLite-backed scenarios

  • Replaces YAML reads in simulations with get_closure_scenario(project).
  • Polls locdatabase(project) modification time for closure changes.
  • Registers <project>ClosureScenarios as a serializable, discoverable table type.

• YAML cleanup

  • Removes yaml from package imports and namespace.
  • Removes closure YAML output mappings.
  • Updates closure simulation tests and generated documentation.

all_closures <- get_closure_scenario(project)

if (is.null(all_closures) || length(all_closures) == 0) {
  stop("No saved closure scenarios found. Run zone_closure() first.")
}