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>

apps/api/schema.gql

@@ -496,6 +496,11 @@ type Mutation {
   Follow a ticket: be told when it moves, is reassigned or gets a comment
   """
   watchIssue(issueId: ID!): CommandResult!
+
+  """
+  Write the release notes (Markdown; null removes them). Also after shipping.
+  """
+  writeReleaseNotes(notes: String, releaseId: ID!): CommandResult!
 }
 
 type MyNotifications {
@@ -743,6 +748,14 @@ type Release {
   """Tickets included in this release"""
   issues(limit: Int! = 100, offset: Int! = 0): IssuePage!
   name: String!
+
+  """What shipped, told for people (Markdown)"""
+  notes: String
+
+  """
+  A Markdown draft of the notes from its finished tickets, by type (not saved)
+  """
+  notesDraft: String!
   progress: ReleaseProgress!
   projectId: ID!
   releasedAt: String