fix(usage): use shared resolveUsedFraction in TUI path, fixing missing remainingFraction fallback

[oldschoola]

Problem

The TUI usage renderer (command-controller.ts) had a local resolveFraction() that was missing the inverted-remaining fallback present in the shared resolveUsedFraction() from @oh-my-pi/pi-ai:

// Shared (usage.ts) — has this:
if (amount.remainingFraction !== undefined)
  return Math.max(0, 1 - amount.remainingFraction);

// Local (command-controller.ts) — was MISSING this

This meant the TUI path failed to resolve a fraction for limits that only populate remainingFraction (no usedFraction, used/limit, or percent+used) — showing an empty bar (·) instead of the correct fill level.

The CLI path (usage-cli.ts) already used the shared function and handled these limits correctly.

Fix

Replaced the local resolveFraction with the shared resolveUsedFraction from @oh-my-pi/pi-ai. This:

• Fixes the missing remainingFraction fallback in the TUI path
• Eliminates the code duplication (4 callsites updated)
• Ensures the TUI and CLI paths resolve fractions identically

Tests

• bun check passes (all 16 packages)
• All usage rendering tests pass (18/18)

[roboomp]

Thanks @oldschoola. lgtm.

Rank: P0. Tight root-cause fix: the local resolveFraction in command-controller.ts was missing the if (amount.remainingFraction !== undefined) return Math.max(0, 1 - amount.remainingFraction) branch that packages/ai/src/usage.ts:101 (resolveUsedFraction) already implements. Verified the two functions are otherwise byte-equivalent against origin/main, so swapping all four callsites onto the shared helper restores the inverted-remaining fallback (e.g. Antigravity/Gemini quotas that only populate remainingFraction) and removes the duplication. CHANGELOG entry under [Unreleased] > Fixed is in place.

No inline findings. The shared helper has existing coverage via the providers in packages/ai/test/* that exercise remainingFraction-only limits; a TUI-side regression test would be nice-to-have but isn't required given the change is a direct delegation.