feat(quota): resolve coding-plan usage windows via the monitor plane

[TriDefender]

Mirror the official desktop panel's two-plane split in the quota snapshot:

• credits plane (existing): zcode-plan billing/balance + preview with the plan JWT — start-plan/trial credit buckets;
• coding plane (new): GET {api.z.ai|open.bigmodel.cn}/api/monitor/usage/ quota/limit with the raw coding-plan API key in authorization (bundle wK/Z_ + md) — data.level + data.limits[] windowed usage rows, surfaced as a Coding group in the TUI card and in the quota CLI / GET /quota.

Behavior fixes from the PR #56 audit:

• a credential without a plan JWT no longer kills the snapshot — credits plane degrades to a noted error while the coding plane still resolves (the card no longer tells logged-in users they are not logged in);
• coding rows render remaining only: live data shows upstream number is not a comparable total (TIME_LIMIT remaining=3894 / number=1), and the official panel likewise never renders X/Y for these windows;
• envelope success semantics mirror the bundle $_ (success !== false and code absent/0/200); monitor failures degrade to codingPlan=null the way the official fetchQuota().catch(() => null) does;
• non-token unitType on balance rows is now visible instead of dropped;
• empty-everything state reworded ("no quota entries reported by upstream").

see _reverse/NOTEPAD.md "coding-plan 用量平面"