feat(ui): project drill-down route with repo-filtered event timeline

Add repo filter param to /v1/events (SQL COALESCE across payload
shapes per source). New /project/:source/* route renders a filtered
activity timeline for a single repo. Dashboard cards link to the
drill-down page.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/moments-api/src/main.rs

@@ -82,6 +82,8 @@ struct EventsQueryParams {
     to: Option<DateTime<Utc>>,
     /// Comma-separated list, e.g. `source=github,gitea`.
     source: Option<String>,
+    /// Filter to a specific repo, e.g. `repo=grenade/moments`.
+    repo: Option<String>,
     limit: Option<u32>,
 }
 
@@ -101,6 +103,7 @@ async fn list_events(
         from: params.from,
         to: params.to,
         sources,
+        repo: params.repo,
         // Public timeline only — private events stay in the DB but are never
         // surfaced. A future authenticated path can flip this.
         include_private: false,