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-entities/src/lib.rs

@@ -67,6 +67,8 @@ pub struct EventQuery {
     pub from: Option<DateTime<Utc>>,
     pub to: Option<DateTime<Utc>>,
     pub sources: Option<Vec<Source>>,
+    /// Filter to events matching a specific repo (matched against payload).
+    pub repo: Option<String>,
     /// When false (default), only `public = true` rows are returned. The API
     /// pins this to false today; a future authenticated path can flip it.
     pub include_private: bool,