feat: release notes

Each release can carry notes in Markdown, written before or after it
ships. A draft is generated from its finished tickets grouped by type, to
edit and copy from the releases page.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

libs/web/tracker/domain/src/lib/ports/gateways.ts

@@ -175,6 +175,13 @@ export abstract class ReleasesGateway {
   ): Observable<CommandResult>;
   abstract archive(releaseId: string): Observable<CommandResult>;
   abstract burnup(releaseId: string): Observable<ReleaseBurnup>;
+  /** A Markdown draft from the release's finished tickets (not saved). */
+  abstract notesDraft(releaseId: string): Observable<string>;
+  /** null removes them. */
+  abstract writeNotes(
+    releaseId: string,
+    notes: string | null,
+  ): Observable<CommandResult>;
 }
 
 export abstract class SprintsGateway {