fix(changelog): resolve embedded notes by semver core (#373)

Whats New and the post-update modal required an exact ## [version] header,
so prerelease package versions (rc, dev) often had no matching section.
Match on major.minor.patch first; if several sections share the core,
prefer a plain X.Y.Z heading when present.

src/utils/changelogReleaseMatch.ts

@@ -0,0 +1,68 @@
+/**
+ * Match CHANGELOG ## [version] sections to the app version from package.json.
+ * Exact match first; otherwise same semver major.minor.patch (ignores -rc, -dev, etc.).
+ */
+
+const SEMVER_CORE = /^v?(\d+\.\d+\.\d+)/i;
+
+export function changelogVersionCore(version: string): string | null {
+  const m = version.trim().match(SEMVER_CORE);
+  return m ? m[1] : null;
+}
+
+function isPlainSemverTriple(header: string): boolean {
+  return /^\d+\.\d+\.\d+$/.test(header.trim());
+}
+
+export function splitChangelogBlocks(changelogRaw: string): string[] {
+  return changelogRaw.split(/\n(?=## \[)/).filter((b: string) => b.startsWith('## ['));
+}
+
+export interface ChangelogReleaseEntry {
+  headerVersion: string;
+  date: string;
+  body: string;
+}
+
+function parseBlock(block: string): ChangelogReleaseEntry | null {
+  const lines = block.split('\n');
+  const m = lines[0].match(/## \[([^\]]+)\](?:\s*-\s*(.+))?/);
+  if (!m) return null;
+  return {
+    headerVersion: m[1],
+    date: (m[2] ?? '').trim(),
+    body: lines.slice(1).join('\n').trim(),
+  };
+}
+
+function headerVersionFromBlock(block: string): string | null {
+  const m = block.match(/^## \[([^\]]+)\]/);
+  return m ? m[1] : null;
+}
+
+export function findChangelogReleaseEntry(
+  changelogRaw: string,
+  appVersion: string,
+): ChangelogReleaseEntry | null {
+  const blocks = splitChangelogBlocks(changelogRaw);
+
+  const exact = blocks.find((b: string) => b.startsWith(`## [${appVersion}]`));
+  if (exact) return parseBlock(exact);
+
+  const appCore = changelogVersionCore(appVersion);
+  if (!appCore) return null;
+
+  const candidates = blocks.filter((b: string) => {
+    const hv = headerVersionFromBlock(b);
+    if (!hv) return false;
+    return changelogVersionCore(hv) === appCore;
+  });
+  if (candidates.length === 0) return null;
+
+  const plain = candidates.find((b: string) => {
+    const hv = headerVersionFromBlock(b);
+    return hv !== null && isPlainSemverTriple(hv);
+  });
+  const chosen = plain ?? candidates[0];
+  return parseBlock(chosen);
+}