feat(web): per-project activity feed at /projects/[key]/activity

Closes Phase 4f from the deferred backlog. Renders every audit_log row
that pertains to a project — memory writes/updates/deletes, snippet
puts/deletes, share grants/changes/revocations, project.identify
collisions — newest first, capped at 150 rows.

Query is a three-leg UNION ALL joining audit_log against memories,
snippets, and the project itself. Avoids relying on payload->>projectKey
which isn't populated consistently across all action shapes.

Each row renders as "<actor> <verb-phrase>" with entity links where
applicable, plus a compact relative timestamp. memory.update entries
also show scope/project transitions inline when those changed. Share
events surface the group name and access level with the existing
tone-coded Badge.

Auth: viewable by anyone with read access to the project (owner +
ro/rw group members). Same guard as the project detail page.

Linked from the project page header so it's discoverable without typing
the URL. No nav-bar link — it's a per-project artifact, not a global
view.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

apps/web/app/(authed)/projects/[key]/page.tsx

@@ -183,6 +183,12 @@ export default async function ProjectDetailPage({
             <Link href="/projects" className="no-underline">
               <Button type="button" variant="secondary">All projects</Button>
             </Link>
+            <Link
+              href={`/projects/${encodeURIComponent(project.key)}/activity`}
+              className="no-underline"
+            >
+              <Button type="button" variant="secondary">Activity</Button>
+            </Link>
             {canWrite ? (
               <Link
                 href={`/memories/new?project=${encodeURIComponent(project.key)}`}