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/Sidebar.tsx

@@ -2,8 +2,7 @@ import { Component, createMemo, createSignal, onMount, Show } from "solid-js";
 import { generateToc, type FileNode, type TocNode } from "../data-loader";
 import { useLocation } from "@solidjs/router";
 import { FileTreeNode, HeadingNode } from "./FileTree";
-import { isPathRevealed } from "./stores/journalStream";
-import { createEffect } from "solid-js";
+import { isPathRevealed } from "./stores/reveal";
 
 export interface SidebarProps {
   isOpen: boolean;