feat(analytics): persist selected time range in localStorage

[jasnoorgill]

Summary

Persists the selected analytics time range (24h / 7d / 30d) in localStorage
so the user lands back on the window they were inspecting after a reload or
new session. Same persistence pattern as the existing theme toggle
(client/index.html) and the freellmapi.locale preference
(client/src/i18n/I18nProvider.tsx).

Storage key: freellmapi.analytics.range. Values are validated against
['24h', '7d', '30d']; invalid or missing entries fall back to the existing
7d default so a corrupted entry never bricks the page. localStorage
access is wrapped in try/catch for SSR / private-mode safety (same
pattern as client/src/lib/api.ts:18-26).

Motivation

The analytics page is a frequent revisit — most operators land on 7d or 30d,
not the default, and a hard reload (or new browser session) always snapped
them back to 7d. Small but persistent annoyance; the existing theme and
freellmapi.locale patterns show the project already considers
client-level preferences worth persisting, so this is consistent with the
project's UX conventions.

Changes

File	Change
client/src/pages/AnalyticsPage.tsx	Added useEffect import; useState<TimeRange>('7d') → useState<TimeRange>(loadStoredRange); new useEffect to persist range on change; added STORAGE_KEY, TIME_RANGES, DEFAULT_RANGE constants and loadStoredRange() helper.

1 file, +34 / -2. No new dependencies. No server changes. No new
migrations. No i18n changes (the tab labels use existing
analytics.range24h / range7d / range30d keys).

Test plan

• npx tsc -b in client/ — clean, 0 errors.
• npx tsc -b in server/ — 9 errors in server/src/routes/keys.ts from
  upstream's multer typing bug (PR I added Agnes AI, but it doesn’t appear in the model list. #438, pre-existing on origin/main
  at 340f414). Not introduced by this PR — same errors reproduce on
  a clean git checkout origin/main.
• npx vitest run in server/ — 524/524 passing, 0 failures, 0 regressions.
• Live verification: deployed on integration/all-my-prs @ f81f781; the
  rebuilt client bundle (dist/assets/index-DJVe5VdN.js) contains the new
  storage key string and the read+set localStorage calls. Restarted
  service, MainPID=860700 running.

Manual smoke:

1. Open /analytics, click 30d.
2. Hard-reload — page opens on 30d (previously: 7d).
3. Open DevTools → Application → Local Storage → key
   freellmapi.analytics.range is 30d.
4. Click 24h, reload — opens on 24h, storage now 24h.
5. Clear the key manually + reload — falls back to 7d.

Compatibility

No breaking changes. The default is unchanged (7d). The persistence is
additive — users who never visit the page see no different behaviour. The
localStorage key is namespaced (freellmapi.*) per the existing
convention.

References operator session 2026-07-04. No upstream issue number yet —
happy to file one if requested.

[jasnoorgill]

Closed in favor of #463 which combines this with the sortable-columns work to avoid rebase churn on the same file.