feat(journal): seed declared variables on initialization

Implement `computeInitialValues` to calculate the starting state of
declared variables and seed them into the journal stream store during
the completions initialization process.

src/components/journal/index.ts

@@ -60,7 +60,7 @@ export { parseDeclareCsv } from "./declare-parser";
 export type { VarDeclaration, TagModifier } from "./declare-parser";
 export { evaluateExpression, expressionIsTag } from "./variable-expression";
 export type { EvalContext, EvalResult } from "./variable-expression";
-export { initReactivity, computeCascade, computeActiveTags, extractDependencies } from "./var-reactivity";
+export { initReactivity, computeCascade, computeActiveTags, extractDependencies, computeInitialValues } from "./var-reactivity";
 export type { VarReactivityState, VariableStore } from "./var-reactivity";
 export { JournalContext, useJournalContext } from "./JournalContext";
 export type { JournalContextValue } from "./JournalContext";