refactor(dashboard): move the summary builder out of its route

src/__tests__/baselines/source-function-lines.json

@@ -1,7 +1,7 @@
 {
   "$comment": "Production functions over 200 lines, keyed \"file :: name\", and their length. Maintained by src/__tests__/source-size-ratchet.test.ts.",
-  "count": 370,
-  "total": 128945,
+  "count": 369,
+  "total": 128339,
   "entries": {
     "app/achievements/page.tsx :: AchievementsPage": 206,
     "app/api/admin/backups/upload/route.ts :: apiHandler(arg)": 314,
@@ -15,7 +15,6 @@
     "app/api/cycle/calendar/route.ts :: apiHandler(arg)": 230,
     "app/api/cycle/day-logs/bulk/route.ts :: postBulk": 213,
     "app/api/cycle/insights/route.ts :: apiHandler(arg)": 226,
-    "app/api/dashboard/summary/route.ts :: buildDashboardSummary": 606,
     "app/api/devices/route.ts :: apiHandler(arg)": 231,
     "app/api/documents/inbound/bulk/route.ts :: apiHandler(arg)": 207,
     "app/api/encounters/[id]/route.ts :: apiHandler(arg) #2": 269,