feat(ui): add /dash route, shared nav, project dashboard with /v1/projects API

Restructure routes: / and /dash show a project overview dashboard,
/activity hosts the existing timeline, /cv remains. Shared Layout
component provides consistent nav header and footer across all routes.

New /v1/projects endpoint aggregates per-repo activity stats (commits,
issues, PRs, date range) from existing event data via SQL. Dashboard
ranks projects by weighted recency + volume score and renders a card
grid.

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

ui/src/api/client.ts

@@ -54,6 +54,17 @@ export interface SourceSummary {
   latest: string | null;
 }
 
+export interface ProjectSummary {
+  repo: string;
+  source: Source;
+  host: string;
+  commit_count: number;
+  issue_count: number;
+  pr_count: number;
+  first_activity: string | null;
+  last_activity: string | null;
+}
+
 export interface EventQuery {
   from?: Date;
   to?: Date;
@@ -82,3 +93,9 @@ export async function fetchSources(): Promise<SourceSummary[]> {
   if (!resp.ok) throw new Error(`sources: HTTP ${resp.status}`);
   return resp.json();
 }
+
+export async function fetchProjects(): Promise<ProjectSummary[]> {
+  const resp = await fetch(`${API_BASE}/projects`);
+  if (!resp.ok) throw new Error(`projects: HTTP ${resp.status}`);
+  return resp.json();
+}