feat: add weekly Sonnet and Opus usage widgets

[shopkinspoint]

Closes #359.

What

Adds two new widgets — weekly-sonnet-usage and weekly-opus-usage — that surface the per-model weekly buckets that the /api/oauth/usage endpoint already returns alongside five_hour and seven_day. These are the same buckets that Claude Code's own /usage panel renders as "Current week (Sonnet only)" / "Current week (Opus)".

Why

For users near (or rate-limited on) Sonnet's weekly cap, the all-models seven_day bar is a strict superset and undercounts Sonnet-specific pressure. The data is already in the response payload — ccstatusline just wasn't reading it.

API response shape, captured against api.anthropic.com today:

{
  "five_hour":         { "utilization": ..., "resets_at": "..." },
  "seven_day":         { "utilization": ..., "resets_at": "..." },
  "seven_day_sonnet":  { "utilization": ..., "resets_at": "..." },
  "seven_day_opus":    { "utilization": ..., "resets_at": "..." }
}

Both per-model buckets can come back as null (e.g. seven_day_opus for accounts that haven't used Opus this week) — the widgets render null in that case, mirroring the existing pattern in WeeklyUsageWidget.

Changes

• src/utils/usage-fetch.ts — extend UsageApiResponseSchema with seven_day_sonnet / seven_day_opus (PerModelWeeklyBucketSchema); thread weeklySonnetUsage / weeklySonnetResetAt / weeklyOpusUsage / weeklyOpusResetAt through parseUsageApiResponse, the cached schema, and parseCachedUsageData so cache files round-trip.
• src/utils/usage-types.ts — add the four new optional fields to UsageData.
• src/types/RenderContext.ts — add the four fields to RenderUsageData.
• src/types/StatusJSON.ts — accept seven_day_sonnet / seven_day_opus in the rate_limits block (the same field names Claude Code passes through).
• src/utils/usage-prefetch.ts — extract the per-model buckets from rate_limits and add weekly-sonnet-usage / weekly-opus-usage to USAGE_WIDGET_TYPES. When a per-model widget is on screen but the prefetch payload lacks the per-model buckets (e.g. older Claude Code release), fall through to the API fetch — single call, then memo-cached like every other usage widget.
• src/utils/usage-windows.ts — add resolveWeeklySonnetUsageWindow / resolveWeeklyOpusUsageWindow. They use the per-model resets_at if present, falling back to seven_day.resets_at (the per-model timestamps are within ~1s of the all-models one, so this is safe).
• src/widgets/WeeklySonnetUsage.ts and src/widgets/WeeklyOpusUsage.ts — new widgets, structurally identical to WeeklyUsage (same display modes, same color, same keybinds), only differing in label and which usageData field they read.
• src/widgets/index.ts and src/utils/widget-manifest.ts — export and register.
• docs/USAGE.md — listed the new widgets in the Tokens/Usage/Context section and the keybind list.

No new dedicated reset-timer widgets

Skipped on purpose. The per-model resets_at matches seven_day.resets_at to within ~1 second in practice (they're computed from the same window boundary), so a separate weekly-sonnet-reset-timer would just duplicate weekly-reset-timer. The new resolvers fall back to weeklyResetAt if the per-model one is absent so the time-cursor mode in the new widgets keeps working when only the legacy bucket is populated.

Tests

$ bun run lint   # tsc + eslint, clean
$ bun test
 1179 pass
 0 fail
 2234 expect() calls
Ran 1179 tests across 105 files.

• src/widgets/__tests__/WeeklySonnetUsage.test.ts and WeeklyOpusUsage.test.ts — mirror WeeklyUsage.test.ts, including the existing runUsagePercentWidgetSuite (which I extended to accept the new field names) and one new case asserting the widget returns null when the per-model bucket is absent.
• src/utils/__tests__/usage-prefetch.test.ts — three new prefetch cases (per-model widgets pull from rate_limits when present; fall through to API fetch when prefetch lacks per-model data; the all-models weekly widget still doesn't require per-model buckets) and three new extractUsageDataFromRateLimits cases (extract per-model buckets, leave fields undefined when buckets absent, treat null per-model buckets as absent).

Smoke test

Custom config exercising all three widgets, fed via bun run src/ccstatusline.ts --config …:

Weekly: 29.0% | Weekly Sonnet: 8.0% | Weekly Opus: 12.0%

When seven_day_opus is null in the payload, the Opus widget renders nothing (existing renderer collapses the surrounding separator).