fix(ui): analytics window preference has no rebrand-migration legacyKey fallback, silently resetting returning users to the 7-day default

[JSONbored]

⚠️ Definition of Done: this issue must be completed in full, in a single PR. Do not split this
work across multiple PRs, and do not defer any Deliverable below to a follow-up issue. A PR that
satisfies only some of the Deliverables, stubs a required test, or leaves a checkbox
partially-done does NOT resolve this issue and will be closed.

Context

apps/loopover-ui/src/routes/app.analytics.tsx:172-175 calls
useLocalStorage<AnalyticsWindowDays>(ANALYTICS_WINDOW_STORAGE_KEY, DEFAULT_ANALYTICS_WINDOW_DAYS)
with no third legacyKey argument.

Two sibling routes correctly supply one: apps/loopover-ui/src/routes/app.runs.tsx:579-583
(useLocalStorage<SavedView[]>("loopover.runs.views", [], "gittensory.runs.views")) and
apps/loopover-ui/src/routes/app.workbench.tsx:33-37
(useLocalStorage<Tab>("loopover.workbench.tab", "miner", "gittensory.workbench.tab")).
apps/loopover-ui/src/lib/use-local-storage.ts's own doc comment explains why: "legacyKey, when
given, is read as a one-time fallback if key is absent (a rebrand key-rename migration)."

ANALYTICS_WINDOW_STORAGE_KEY was itself renamed from "gittensory.analytics.windowDays" to
"loopover.analytics.windowDays" in the same rebrand commit (75450f1d5) that added the
legacyKey migration pattern to other files — this file was simply missed.
grep -rn "gittensory.analytics" . returns zero hits anywhere else in the repo, confirming no
alternate migration path exists for this specific key.

Consequence: any user who had picked a 30-day or 90-day analytics window before the rebrand cutover
silently loses that preference and reverts to the 7-day default on their next visit, with no error
and no indication anything changed.

Requirements

• Add the legacy key "gittensory.analytics.windowDays" as the third useLocalStorage argument in
  app.analytics.tsx, matching the pattern already used by app.runs.tsx/app.workbench.tsx
  exactly.

Deliverables

• app.analytics.tsx's useLocalStorage call for the analytics window preference includes the
  "gittensory.analytics.windowDays" legacy key.
• A new test seeds localStorage["gittensory.analytics.windowDays"] = "30", mounts
  ProductAnalytics, and asserts the toggle group shows 30d selected and
  localStorage["loopover.analytics.windowDays"] is backfilled — mirroring the existing
  migration tests already used for app.runs.tsx/app.workbench.tsx in use-local-storage.test.ts.

Both Deliverables are required in the same PR.

Test Coverage Requirements

apps/** is excluded from codecov/patch gating, but apps/loopover-ui's own local vitest
coverage thresholds apply — the new test must exercise the previously-missing migration path
directly.

Expected Outcome

A returning user's pre-rebrand analytics window preference is correctly migrated forward instead of
silently reverting to the default, matching the migration guarantee already provided for the runs
and workbench view preferences.

Links & Resources

• apps/loopover-ui/src/routes/app.analytics.tsx:172-175 (the fix location)
• apps/loopover-ui/src/routes/app.runs.tsx:579-583, app.workbench.tsx:33-37 (the already-correct
  sibling pattern)
• apps/loopover-ui/src/lib/use-local-storage.ts (legacyKey doc comment)
• apps/loopover-ui/src/lib/use-local-storage.test.ts (existing migration-test pattern to mirror)
• Introduced/renamed by commit 75450f1d5

[linear-code]

JSO-6041