fix(web): show selected model in context window tooltip

[nqrwhal]

Fixes #4770.

What Changed

The context-window tooltip now resolves its compaction label from the active thread's exact provider instance and selected model. It uses the same short display name as the model picker, falls back to the selected model slug when metadata is unavailable, and uses neutral copy when there is no model selection.

A focused regression test covers multiple instances of the same driver, including two instances that expose the same model slug with different display metadata.

Why

The tooltip previously found the selected provider instance and then passed only its driver to getProviderDisplayName. That driver-scoped lookup resolves the default/first instance, so a thread using another Codex profile could show an unrelated instance name such as Yufei Pro 20x.

Describing compaction with the selected model is accurate and matches the model picker already visible beside the context meter. This keeps the change scoped to presentation logic; context accounting and provider behavior are unchanged.

UI Changes

Before	After
The tooltip names an unrelated provider instance.	The tooltip names the selected model shown in the composer.

Validation

• vp test run apps/web/src/components/chat/ContextWindowMeter.logic.test.ts — 4 tests passed
• vp run --filter @t3tools/web typecheck
• vp fmt --check apps/web/src/components/chat/ChatComposer.tsx apps/web/src/components/chat/ContextWindowMeter.tsx apps/web/src/components/chat/ContextWindowMeter.logic.ts apps/web/src/components/chat/ContextWindowMeter.logic.test.ts
• vp lint --report-unused-disable-directives apps/web/src/components/chat/ChatComposer.tsx apps/web/src/components/chat/ContextWindowMeter.tsx apps/web/src/components/chat/ContextWindowMeter.logic.ts apps/web/src/components/chat/ContextWindowMeter.logic.test.ts
• git diff HEAD^ --check
• Isolated web-app pass using the repository's test-t3-app workflow: the rendered tooltip read Context for Claude Fable 5 compacts automatically when needed. while the composer model trigger also showed Claude Fable 5.

Checklist

• This PR is small and focused
• I explained what changed and why
• I included before/after screenshots for the UI change
• No animation or interaction change requires a video

Note

Show selected model name in context window tooltip instead of provider name

• Replaces provider display name with model display name in the ContextWindowMeter tooltip, using the model's shortName when available and falling back to the model slug.
• Adds resolveContextWindowModelDisplayName in ContextWindowMeter.logic.ts to resolve the display name tied to the exact provider instance.
• Updates the compaction message from 'It compacts automatically...' to 'Context for <model> compacts automatically when needed.' (or a neutral fallback when no model name is available).

^{Macroscope summarized 6348438.}

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[macroscopeapp]

Approvability

Verdict: Approved 6348438

This PR makes a simple UI text change in the context window tooltip, switching from showing provider name to model name. The change is well-tested, self-contained, and has no runtime behavior impact beyond display text.

^{You can customize Macroscope's approvability policy. Learn more.}

Dismissing prior approval to re-evaluate e52f650

[macroscopeapp]

One finding: the compaction hint in ContextWindowMeter swaps the themed text-secondary-label token for text-muted-foreground/70, which bypasses the custom-theme token bridge and lowers contrast. Details inline.

^{Posted via Macroscope — UI Consistency}

Dismissing prior approval to re-evaluate 6348438