Accounts: show Claude's per-model weekly limits (Fable)

[and-human]

Summary

• Claude accounts now show per-model weekly caps (today: Fable) as an extra meter under Session and Week.
• Why: /api/oauth/usage reports model caps only in its limits list (kind: "weekly_scoped", scope.model.display_name). The legacy seven_day_opus / seven_day_sonnet keys come back null. Zeron only read five_hour and seven_day, so an account at 85% of its Fable cap showed "Week 70%" and looked like it had room.
• The footer ring already shows the most-used window, so it now follows the cap that actually binds.
• The footer popover and the Settings → Accounts list both capped meters at 2. That cap is now MAX_USAGE_METERS = 3. Side effect: Copilot Free can now show its third quota (Completions) as well.
• Engine-only parsing, no proto or doc changes. Rows without a model display name (for example surface-scoped limits) are skipped.

Test plan

• New unit test claude_usage_windows_add_per_model_weekly_limits, built from the response shape seen live (null legacy keys, limits with session / weekly_all / weekly_scoped).
• cargo test -p zeron-engine --lib claude_usage_windows: 3 passed.
• Checked the live endpoint on two Max 20× accounts. One returned weekly_scoped Fable at 85% (severity: warning) while seven_day was 70%.
• Manual: dev build (ZERON_DATA_DIR=~/.zeron-dev) Settings → Providers → Claude Code → Accounts shows Session 23% / Week 70% / Fable 85% (warning color) for the live account.
• Manual: footer popover not captured. It uses the same render_usage_meter and the same cap.
• cargo clippy -p zeron-engine -p zeron-ui --all-targets: no new warnings.

Screenshots

Before (footer popover, v0.2.103): Week 70%, no Fable row

(image to attach)

After (Settings → Accounts, dev build): Fable 85% shown in warning color

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