Binary-search the two ellipsis truncation strips

[zangjiucheng]

renderContent truncates long text by stripping one character at a time and re-measuring, at main.ts:638 and :648.

This is a tail-latency cliff on repositories with long commit subjects or narrow columns — not a flat cost on every frame, and it should not be sold as one. A binary search over the cut point replaces a linear scan with a logarithmic one.

Gate the change on a before/after DEV HUD number measured on a repository that actually triggers it.

Sibling: #87 covers the deterministic hoists in the same function.

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_{Found during v1.3.0 research: parallel codebase surveys, then each finding independently verified against the code before filing. Line numbers are from dev at the time of writing.}