Fix weekly usage period labels

[FZ2000]

Why

The 90-day and all-time usage APIs resolve granularity=auto to weekly buckets, but the macOS Usage pane treated every returned bucket as a day. The summary could say 13/14 Active days, while the chart and its accessibility controls still said Cost per day, Previous usage day, and this day's value.

Central change

The Usage pane now derives every period-unit label from the API's effective filters_echo.granularity: daily responses use day copy, weekly responses use week copy, and unknown or legacy payloads use neutral period copy rather than guessing.

What changed

• Decode the usage summary's effective granularity.
• Share one period presentation across the activity summary, chart title, navigation labels, and selection hint.
• Preserve the existing active-bucket calculation and existing chart automation identifier.
• Add a deterministic 90-day fixture with 14 Monday-based weekly buckets, including one inactive week.
• Pair the selected range and its matching summary in snapshot state so stale 7-day data cannot wear a 90d label.
• Extend the Usage render matrix from six to eight artifacts with 2240×2240 weekly light/dark references.

Visual contract

The two new canonical references visibly cover:

• Recorded use · 90d and the selected 90d range chip;
• Active weeks 13/14;
• Cost per week;
• 14 weekly bars, including the inactive week; and
• unclipped light and dark layouts.

Both PNGs were generated on the pinned canonical renderer, immediately re-verified, and reviewed directly. The six existing Usage references remain unchanged.

Review order

1. DashboardModel.swift and UsagePane.swift: effective-granularity decoding and the shared period presentation.
2. UsagePeriodPresentationTests.swift: daily, weekly, empty, unknown, and legacy semantics, including chart/accessibility copy.
3. DashboardStore.swift, DashboardSnapshotHarness.swift, UsageSnapshotHarness.swift, and dashboard.json: deterministic 7-day/90-day state wiring.
4. UsageSnapshotHarnessTests.swift and UsageVisualRegressionTests.swift: eight-artifact render contract.
5. The two usage-weekly-reference-*.png files: final visual evidence.

Safety

• No backend behavior or query construction changes.
• Daily copy and the six existing Usage pixels are unchanged.
• Unknown granularity fails neutral instead of inventing a unit.
• The range and response are injected as one snapshot value.
• The branch was merged with current main without conflicts, then re-verified.

Verification

Red evidence established before implementation:

• The deterministic harness expected eight artifacts but rendered only six; both weekly files were missing.
• The canonical verifier failed only for the missing weekly light/dark references.
• Period tests failed because no shared daily/weekly chart presentation existed.

Final integrated tree:

• swift test — 151 passed; 6 visual wrappers intentionally delegated to the canonical verifier
• swift build -c release — passed
• python -m pytest tests/test_tokens_explorer.py::test_usage_summary_whitelist_validation_and_granularity_override — passed
• ./Scripts/visual-snapshots verify — About, Dashboard, Menu, Setup, eight-state Usage, and Work references all match
• Weekly fixture audit — 14 Mondays; period/client session, token, and cost totals reconcile
• git diff origin/main --check — passed