feat: replace calendar day modal with dedicated day-view page

Calendar day clicks now navigate to /experiments/:id/day/:date
(with ?field= param). ExperimentDayView shows a sticky-column table
of all subjects with data that day, inline edit via modal, and a
session-metrics bar chart from analysis_summary. Subject name links
to /daily-statuses/:id. Backend adds ?date= filtering to
GET /experiments/:id/daily-statuses.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/api/client.js

@@ -34,6 +34,7 @@ export const experimentsApi = {
   getSubjectTemplate: (id) => api.get(`/experiments/${id}/subject-template`).then((r) => r.data),
   updateSubjectTemplate: (id, template) => api.put(`/experiments/${id}/subject-template`, template).then((r) => r.data),
   getDailyStatuses: (id) => api.get(`/experiments/${id}/daily-statuses`).then((r) => r.data),
+  getDayStatuses: (id, date) => api.get(`/experiments/${id}/daily-statuses`, { params: { date } }).then((r) => r.data),
   getCalendar: (id, field) => api.get(`/experiments/${id}/calendar`, { params: { field } }).then((r) => r.data),
 };