fix(web): only show Codex Fast badge for fast tier

[swear01]

Closes #1004

Summary

• remove the Codex Fast badge heuristic based on model names and reasoning effort
• show Fast only when the explicit session service tier is Fast
• add regressions for low reasoning, mini models, Fast, and Standard

Why

Codex /fast is a distinct service tier. Low reasoning and mini model variants must not be presented as Fast mode.

Validation

• retroactive test-only check on upstream/main: 2 expected failures (low reasoning and mini model were mislabeled Fast)
• bun run --cwd web test -- src/components/AssistantChat/StatusBar.test.tsx — 6 passed
• real Chromium render smoke:
  • low reasoning + unset tier — no Fast badge
  • mini model + unset tier — no Fast badge
  • explicit Fast tier — Fast badge shown
  • explicit Standard tier — no Fast badge
• repository typecheck passed
• local non-runner suites passed: CLI 1103, Hub 453, Web 1135, Shared 105
• GitHub Actions test passed on the PR head
• git diff --check

[github-actions]

Findings
No issues found in the added or modified lines.

Summary
Review mode: initial
Reviewed the full PR diff for the StatusBar Fast badge change and the replacement TSX test coverage. The change now gates the badge on the explicit stored Codex service tier, consistent with the existing fast/standard schema and the composer service-tier flow. Residual risk: I did not execute tests in this automation review.

Testing
Not run (automation)

HAPI Bot

[github-actions]

Findings
No issues found in the added or modified lines.

Summary
Review mode: follow-up after new commits
Reviewed the full current PR diff for the StatusBar Fast badge change and the TSX test replacement. The badge now follows the same explicit serviceTier === 'fast' semantics used by SessionHeader, and the added tests cover unset tier, mini-model heuristic removal, explicit fast, and explicit standard. Residual risk: I did not execute tests in this automation review.

Testing
Not run (automation)

HAPI Bot