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/index.ts

@@ -60,7 +60,7 @@ export { parseDeclareCsv } from "./declare-parser";
 export type { VarDeclaration, TagModifier } from "./declare-parser";
 export { evaluateExpression, expressionIsTag, exprValueToString } from "./variable-expression";
 export type { EvalContext, EvalResult, ExprValue } from "./variable-expression";
-export { initReactivity, computeCascade, getCombined, getMods, getDeclExpr, setBase, extractDependencies, computeInitialValues } from "./var-reactivity";
-export type { VarReactivityState, VariableStore } from "./var-reactivity";
+export { initReactivity, computeCascade, getCombined, getMods, getDeclExpr, setBase, extractDependencies, computeInitialValues, getReactivityDiagnostics, clearReactivityDiagnostics, onReactivityDiagnostics } from "./var-reactivity";
+export type { VarReactivityState, VariableStore, ReactivityDiagnostic } from "./var-reactivity";
 export { JournalContext, useJournalContext } from "./JournalContext";
 export type { JournalContextValue } from "./JournalContext";