[Story] FEAT-USER-GROUPS-09: Notifications on Newly Gained Group Access

[sven1103-agent]

Parent Feature

#1558

User Story

As a user, I want to be notified only about project access I newly gain through a group, so that
I know I can now work on those projects without receiving spam when nothing changes for me.

Acceptance Criteria

• Given I am newly added to a group shared on a project, When the group or project grant is
  created, Then I receive a single email per project I newly gain access to (deduplicated across
  multiple groups and roles).
• Given I join a group that is already shared on several projects I previously had no access to,
  When the join happens, Then I receive a digest email listing exactly those projects.
• Given a group grant changes my role on a project but I already had access, When the role changes,
  Then I do not receive a newly-gained-access email (role-level changes stay audit-log-only), and
  project owners/admins are informed of the membership change per policy.

Requirement IDs: GROUP-R-10

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EPIC 5 — UI surfaces

Definition of done: My Groups view (account area), Admin Groups view, Project Access page
Groups section, share-dialog group tab, and project cards showing group names all exist and
enforce the visibility policy.

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Tracking

• Epic: EPIC 4 — Notifications
• Stable Story ID: FEAT-USER-GROUPS-09
• Source: docs/features/FEAT-USER-GROUPS-stories.md — PO-approved (2026-09-22)