feat: comments marked as decisions, on top of the ticket and searchable

Whoever can change the ticket flags a comment as a decision (new event
CommentDecisionMarkedEvent on the comment). The ticket page lists its
decisions above the description, with a link to the comment in the
conversation (`?comment=<id>` scrolls to it and points at it), and the
search palette finds them by their text across my projects.

API: markDecision / PUT-DELETE /api/comments/{id}/decision; Issue.decisions
and GET /api/issues/{issue}/decisions; decisions(projectId?, search) and
GET /api/projects/{project}/decisions, GET /api/me/decisions. MCP:
mark_decision, search_decisions, and get_issue includes them.

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

apps/api/schema.gql

@@ -270,6 +270,13 @@ type Comment {
   """Empty on a deleted comment kept for its replies"""
   body: String!
   createdAt: String!
+  decidedAt: String
+
+  """Who marked it as a decision"""
+  decidedBy: UserRef
+
+  """Marked as a decision of the ticket (shown above it)"""
+  decision: Boolean!
 
   """Deleted, but kept (without its text) while it has replies"""
   deleted: Boolean!
@@ -475,6 +482,12 @@ type DashboardShare {
   token: String!
 }
 
+"""A comment marked as a decision, with its ticket"""
+type Decision {
+  comment: Comment!
+  issue: IssueParent!
+}
+
 """A commit, branch or pull request that mentions the ticket"""
 type DevLink {
   at: String!
@@ -640,6 +653,9 @@ type Issue {
 
   """Values of the project's custom fields (only those set)"""
   customFields: [CustomFieldValue!]!
+
+  """Its comments marked as decisions, oldest first"""
+  decisions: [Comment!]!
   description: String
 
   """Commits, branches and pull requests that mention it"""
@@ -973,6 +989,11 @@ type Mutation {
   """Relate tickets, e.g. FE DEPENDS_ON BE, QA TESTS FE"""
   linkIssues(input: LinkIssuesInput!): CommandResult!
 
+  """
+  Mark a comment as a decision of its ticket, or unmark it (on: false). Whoever can change the ticket
+  """
+  markDecision(commentId: ID!, on: Boolean! = true): CommandResult!
+
   """Mark these as read, or all of them when `ids` is omitted"""
   markNotificationsRead(ids: [ID!]): Boolean!
 
@@ -1491,6 +1512,11 @@ type Query {
   """The project's link for clients, if any (owners and admins)"""
   dashboardShare(projectId: ID!): DashboardShare
 
+  """
+  Decisions by their text, most recent first: of a project, or of all my projects without one
+  """
+  decisions(limit: Int! = 20, projectId: ID, search: String): [Decision!]!
+
   """
   A project's epics: top-level tickets that group others, with the progress of those
   """