Status bar: show context window % used alongside token count

Question

## Feature Request

**What:** Display the percentage of the context window consumed next to the token count in the status bar.

**Current behavior:** The status bar shows raw token count (e.g., `1,234 tokens`).

**Desired behavior:** Show percentage alongside it (e.g., `1,234 tokens (6%)`), so users can quickly gauge how close they are to the context limit without doing mental math.

**Why:** Token count alone is hard to interpret without knowing the model's context window size. A percentage giv