fix(journal): surface variable eval errors

Collect and report failed declarations, failed tag modifier expressions, and
circular dependencies instead of swallowing them. Diagnostics are deduped,
logged with key/expression context, cleared on re-init, and exposed through
useJournalCompletions and the VariableView warning banner. A bad declaration
no longer aborts the rest of a cascade.

Reject malformed numeric literals in the tokenizer so inputs like "1.2.3"
throw instead of being truncated by parseFloat.

src/components/journal/VariableView.tsx

@@ -17,6 +17,9 @@ export const VariableView: Component = () => {
 
   const values = createMemo(() => stream.variables);
 
+  /** Runtime engine diagnostics (bad declarations / modifiers). */
+  const diagnostics = createMemo(() => comp.diagnostics());
+
   /** Flat list of all variables */
   const items = createMemo(() => {
     const vars = values();
@@ -32,6 +35,20 @@ export const VariableView: Component = () => {
 
   return (
     <div class="h-full overflow-y-auto bg-gray-50">
+      <Show when={diagnostics().length > 0}>
+        <div class="border-b border-amber-200 bg-amber-50 px-3 py-2">
+          <div class="text-xs font-semibold text-amber-800 mb-1">
+            变量求值有 {diagnostics().length} 个问题
+          </div>
+          <ul class="space-y-1">
+            <For each={diagnostics()}>
+              {(d) => (
+                <li class="text-xs text-amber-700 font-mono break-all">{d.message}</li>
+              )}
+            </For>
+          </ul>
+        </div>
+      </Show>
       <Show
         when={hasAnyData()}
         fallback={