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>

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

@@ -358,6 +358,8 @@ export abstract class SprintsGateway {
 
 export abstract class ActivityGateway {
   abstract list(projectId: string, issueId?: string): Observable<Activity[]>;
+  /** What happened that day (`YYYY-MM-DD`, UTC), newest first (200 at most). */
+  abstract onDay(projectId: string, day: string): Observable<Activity[]>;
 }
 
 export abstract class UsersGateway {