perf: server-side caching + remove bulk status fetch from experiment page

- Add backend/src/lib/cache.js — in-process TTL Map cache with
  prefix-based invalidation; no external dependencies

- Cache /experiments/:id/calendar?field=X per (experimentId, field).
  Invalidated immediately on any DailyStatus write.

- Cache /experiments/:id/daily-statuses per (experimentId, date, analysisOnly).
  Invalidated immediately on any DailyStatus write (create/update/delete
  and analysis-summary saves all clear the relevant prefix).

- Add ?analysisOnly=true to /daily-statuses: filters rows where
  analysis_summary IS NOT NULL. Charts are the only consumer and already
  discard rows without analysis data; pre-filtering server-side avoids
  sending the full status payload (71 rows → 1 for this experiment).

- ExperimentCalendar: remove allStatuses prop, fetch calendar data
  directly via API. The component now issues one small GET per field
  selection change instead of the parent loading thousands of rows upfront.

- ExperimentDetail: pass analysisOnly:true to getDailyStatuses;
  drop allStatuses prop from ExperimentCalendar. Cold experiment page
  load no longer fetches every daily status record.

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

frontend/src/pages/ExperimentDetail.jsx

@@ -95,7 +95,9 @@ export default function ExperimentDetail() {
         animalsApi.list(id),
         experimentsApi.getSubjectTemplate(id),
         experimentsApi.getTemplate(id),
-        experimentsApi.getDailyStatuses(id),
+        // Only fetch statuses that have saved analysis_summary — charts are the only consumer,
+        // and they filter for analysis_summary.total != null anyway.
+        experimentsApi.getDailyStatuses(id, { analysisOnly: true }),
       ]);
       setExperiment(exp);
       setAnimals(anims);
@@ -371,7 +373,6 @@ export default function ExperimentDetail() {
         <ExperimentCalendar
           experimentId={id}
           template={dailyTemplate}
-          allStatuses={experimentStatuses}
         />
       )}