chore(changelog): retire CHANGELOG.md as a dependency

The update dialog (server and desktop) now reads changelog/index.json and
renders title, intro and groups; the release workflow builds the GitHub
Release body and name from changelog/<version>.md; oc-dev, the issue-intake
agent, AGENTS.md and the changelog skill no longer point at the file.

CHANGELOG.md stays as a legacy copy for installs up to 1.22.1, which fetch
it for update notes. The generator refreshes it while it exists and never
recreates it, so deleting it after 2026-09-19 retires it for good.

Generated outputs hold released versions only, so editing unreleased.md
never makes them stale: agents write that file and nothing else, and
oc-dev create-release does the generation.

Claude-Session: https://claude.ai/code/session_01VqV56Hez25hTxXH4ipJfzH

packages/web/server/lib/changelog/update-notes.js

@@ -0,0 +1,82 @@
+// Release notes for the update dialog.
+//
+// The repo publishes `changelog/index.json` on `main`: one object per release,
+// newest first, with the app notes grouped as New / Improvements / Fixes /
+// Misc. This module fetches it and renders the releases between the installed
+// version (exclusive) and the offered one (inclusive) as the Markdown the
+// dialog already understands: a `## [x.y.z] - YYYY-MM-DD` header per release,
+// the release title in bold, the intro, then the groups.
+//
+// Any failure (network, 404, unexpected shape) yields null: the update is
+// still offered, only without notes.
+
+export const CHANGELOG_INDEX_URL = 'https://raw.githubusercontent.com/openchamber/openchamber/main/changelog/index.json';
+
+const GROUPS = [
+  ['new', 'New'],
+  ['improvements', 'Improvements'],
+  ['fixes', 'Fixes'],
+  ['misc', 'Misc'],
+];
+
+const VERSION_PATTERN = /^\d+\.\d+\.\d+$/;
+const DATE_PATTERN = /^\d{4}-\d{2}-\d{2}$/;
+
+// The file crosses a network boundary with no schema library on this side, so
+// each field is coerced into its domain shape here; a release without a valid
+// version and date is dropped.
+const text = (value) => (value === null || value === undefined ? null : String(value).trim() || null);
+const bulletList = (value) => (Array.isArray(value) ? value.map((item) => String(item)) : []);
+
+const parseRelease = (entry) => {
+  if (entry === null || entry === undefined) return null;
+  const version = text(entry.version);
+  const date = text(entry.date);
+  if (!version || !VERSION_PATTERN.test(version) || !date || !DATE_PATTERN.test(date)) return null;
+  const app = entry.app ?? {};
+  return {
+    version,
+    date,
+    title: text(entry.title),
+    intro: text(entry.intro),
+    groups: GROUPS.map(([key, heading]) => ({ heading, bullets: bulletList(app[key]) })),
+  };
+};
+
+const renderRelease = (release) => {
+  const lines = [`## [${release.version}] - ${release.date}`, ''];
+  if (release.title) lines.push(`**${release.title}**`, '');
+  if (release.intro) lines.push(release.intro, '');
+  for (const { heading, bullets } of release.groups) {
+    if (bullets.length === 0) continue;
+    lines.push(`### ${heading}`, '', ...bullets.map((bullet) => `- ${bullet}`), '');
+  }
+  return lines.join('\n').trim();
+};
+
+/**
+ * Markdown for the releases in (fromVersion, toVersion], newest first, or
+ * null when the index holds none of them.
+ */
+export function renderUpdateNotes(index, fromVersion, toVersion, compareVersions) {
+  if (!Array.isArray(index)) return null;
+  const relevant = index
+    .map(parseRelease)
+    .filter((release) => release !== null)
+    .filter((release) => compareVersions(release.version, fromVersion) > 0 && compareVersions(release.version, toVersion) <= 0)
+    .sort((a, b) => compareVersions(b.version, a.version));
+  if (relevant.length === 0) return null;
+  return relevant.map(renderRelease).join('\n\n');
+}
+
+/** Fetch the index and render the notes for one update; null on any failure. */
+export async function fetchUpdateNotes(fromVersion, toVersion, compareVersions, options = {}) {
+  const fetchImpl = options.fetch ?? fetch;
+  try {
+    const response = await fetchImpl(CHANGELOG_INDEX_URL, { signal: AbortSignal.timeout(options.timeoutMs ?? 10_000) });
+    if (!response.ok) return null;
+    return renderUpdateNotes(await response.json(), fromVersion, toVersion, compareVersions);
+  } catch {
+    return null;
+  }
+}