[FEATURE] Persist usage-banner dismissal across increments and multiple VSCode instances

Problem Statement

Dismissing the usage-limit banner ("You've used 83% of your usage credit limit · resets in 8d") only hides that one instance:

1. Every percent increment re-triggers it. Dismissed at 80%, it came back at 81%, 82%, 83%, and 84% ... five dismissals in one working stretch, none carrying new information.
2. Dismissal is per-window. With multiple VS Code windows open, each one has to be dismissed separately.

Proposed Solution

Alongside the threshold/opt-out proposed in #72994, make dismissal part of the same configuration:

• whether a dismissed banner re-notifies at all for the rest of the usage window
• if it does, the step ... increments of 5 or 10 percent, not every percent

Dismissal state should be account-level, not per-window, so one dismissal covers all open windows and sessions.

Environment

• Claude Code: VS Code extension
• OS: macOS

Screenshot

<img width="978" height="193" alt="Image" src="https://github.com/user-attachments/assets/0d3b03b8-7bec-4f21-8b4d-8e5c390352d5" />