refactor: extract persistence and reveal logic into new stores

Move localStorage and URL parameter management from `journalStream`
to a dedicated `persistence` store. Relocate DOM reveal and heading
injection logic to a new `reveal` store to improve separation of
concerns.

src/components/journal/JournalInput.tsx

@@ -21,6 +21,7 @@ import {
   Match,
 } from "solid-js";
 import { sendMessage, useJournalStream } from "../stores/journalStream";
+import { linkPrefill, setLinkPrefill } from "../stores/reveal";
 import { useJournalCompletions, ensureCompletions } from "./completions";
 import { resolveRollPayload } from "./types/roll";
 
@@ -88,6 +89,16 @@ export const JournalInput: Component = () => {
     void ensureCompletions();
   });
 
+  // Listen for /link prefill requests from article headings
+  createEffect(() => {
+    const prefilled = linkPrefill();
+    if (prefilled) {
+      setText(prefilled);
+      setLinkPrefill(null);
+      textareaRef?.focus();
+    }
+  });
+
   // ---- Send ----
 
   function handleSend() {