feat: add usage tracking API and /usage dialog

[IgorWarzocha]

What does this PR do?

Adds a usage tracking API + TUI dialog for authenticated providers, including Codex and Copilot (using current OAuth implementation as of 1.1.13).

• Adds /usage server route plus shared Usage module for fetching, caching, and normalizing usage snapshots
• Captures Codex rate-limit headers and 429s to update usage state
• Adds /usage autocomplete handling and a unified usage dialog (plan/quota parsing, scaling, reset display)
• Regenerates SDK/OpenAPI artifacts for the new endpoint

How did you verify your code works?

• Manual testing: verified with Copilot OAuth on free tier; GPT account on Plus plan; further provider/plan tests needed
• bun run typecheck (fails in packages/opencode/src/server/server.ts:202 due to existing deep type instantiation error; unchanged from upstream)

screenrecording-2026-01-11_18-37-51.mp4

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on my search results, I found 2 highly related PRs that appear to address similar or overlapping functionality:

Potential Duplicates:

1. PR feat: display Anthropic and OpenAI OAuth usage in status dialog and sidebar #6905: feat: display Anthropic and OpenAI OAuth usage in status dialog and sidebar

   • Related because it also implements usage tracking and display for authenticated providers (Anthropic and OpenAI) in a dialog/sidebar context

2. PR feat: Add (z.ai) plan usage tracking in the sidebar #6298: feat: Add (z.ai) plan usage tracking in the sidebar

   • Related because it implements usage/plan tracking display functionality for another provider

These PRs implement similar functionality (usage display for providers), though PR #7837 appears to be a more comprehensive solution with a dedicated /usage API endpoint and unified dialog supporting multiple providers (Codex and Copilot).