feat(workflow): reject execution plans that reference unknown tools

A freestyle stage's tools are LLM-authored in the execution_plan. At run time an
unresolvable tool name is silently dropped (resolve -> null -> mapNotNull), so the
stage runs toolless — e.g. a misspelled task_update means the implementation stage
quietly loses task tracking, invisible without a live run.

ExecutionPlanCompiler now takes the registered-tool universe and rejects a plan that
names an unknown tool, with a message identifying the tool and stage. FreestyleDriver
already turns a compile failure into a rejection the architect retries. The param
defaults to empty (validation skipped) so existing callers are unaffected; Main feeds
it toolRegistry.all().

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/server/src/main/kotlin/com/correx/apps/server/Main.kt

@@ -457,7 +457,7 @@ fun main() {
 
     val freestyleDriver = FreestyleDriver(
         eventStore = eventStore,
-        compiler = ExecutionPlanCompiler(artifactKindRegistry),
+        compiler = ExecutionPlanCompiler(artifactKindRegistry, toolRegistry.all().map { it.name }.toSet()),
         planContent = { sid -> orchestrator.validatedArtifactContent(sid, ArtifactId("execution_plan")) },
         config = defaultOrchestrationConfig,
         runPhase2 = { sid, graph, cfg -> orchestrator.run(sid, graph, cfg) },