feat: a day of the activity map opens what happened, ticket by ticket

On the project dashboard, a day with activity can be picked on the map:
a side panel lists that day's moves grouped by ticket (each key opens
it), with the time of each, and the project's own (sprints, releases,
members) apart.

The activity feed takes an `after` date (GraphQL, REST), so with
`before` it reads a window such as a day; the MCP's
get_project_activity takes a `day`.

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

apps/api/schema.gql

@@ -1464,6 +1464,11 @@ type Quality {
 type Query {
   """Project activity feed (newest first)"""
   activity(
+    """
+    ISO date: only activity at or after it (with before, a window such as a day)
+    """
+    after: String
+
     """ISO date cursor"""
     before: String
     issueId: ID