fix(web): clarify fast mode availability in settings

[mariusdill]

Provider settings currently show Fast mode whenever a model offers a speed option, even when Fast mode is off. This looks like an active setting. The label now says Fast mode available to describe the capability accurately.

This is a small wording fix for an obvious ambiguity. Capability detection, model defaults, picker visibility, and runtime settings are unchanged. The composer continues to describe active Fast mode separately. Web and desktop share this component; mobile has no equivalent capability label.

Verification:

• A temporary Node assertion against the actual capability-description function failed before the fix and passed afterwards with fastMode.currentValue both false and true.
• vp test run --project unit src/components/settings/ProviderModelsSection.test.ts: 3 tests passed (existing ordering and bulk visibility coverage).
• vp exec tsc --noEmit in apps/web: passed.
• Targeted vp lint and vp fmt --check: passed; lint reports an existing effect-dependency warning on line 224.
• Before/after captures render the actual ProviderModelsSection in a temporary Vite harness at 1280 × 800 with Fast mode off. The harness was removed and is not committed. Full app navigation, narrow layouts, and the installed desktop build were not tested.
• Independent read-only review by Opus 5.5 (high): no concrete defects found.

Before:

After:

Made by GPT-6.1 Sol (medium) in T3 Code through the Codex harness.

[macroscopeapp]

Approvability

Verdict: Approved at 7d79245

Macroscope's review found this PR approvable — This PR only clarifies an existing settings label from “Fast mode” to “Fast mode available.” Capability detection, defaults, and runtime behavior remain unchanged, making the change a small, isolated UI wording adjustment.

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