controllogic: make expr evaluator value-polymorphic (arrays, indexing, array funcs)

Rewrites internal/controllogic/expr.go to evaluate to Value (scalar float64
or []Value array): adds array literals [a,b], postfix indexing arr[i], and
array functions (len, sum, mean, push, pop, slice, concat, sort, …). Resolver
type changes from func(...) float64 to func(...) Value; EvalValue added;
EvalExpr/EvalBool retain scalar float64/bool returns. Three temporary shims
added in engine.go, lua.go, and expr_test.go pending Tasks 4 and 6.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/controllogic/engine.go

@@ -897,7 +897,7 @@ func (cg *compiledGraph) activate(triggerID string) {
 		dt = float64(now-last) / 1e9
 	}
 
-	resolve := func(ds, name string) float64 {
+	resolve := func(ds, name string) Value { // shim: was float64 (Task 4 removes)
 		switch ds {
 		case "sys":
 			if name == "dt" {