feat(tui): right-align the token meter legend's rates in their column

[edwin-zvs]

Follow-up to #1063. The grid aligned the names; the rates still trailed them, so each figure started wherever its name happened to stop.

--- before (rate trails the name) ---
|● claude-opus-5 4.8k/s   ● claude-sonnet-5 1.2k/s |
|● gpt-5.5-codex idle     ● grok-4 310/s           |
|● gemini-3-pro 90/s      ● claude-haiku-4-5 idle  |
|● qwen3-coder 2.4k/s     |

--- after (rate against the cell edge) ---
|● claude-opus-5   4.8k/s ● claude-sonnet-5 1.2k/s |
|● gpt-5.5-codex     idle ● grok-4           310/s |
|● gemini-3-pro      90/s ● claude-haiku-4-5  idle |
|● qwen3-coder     2.4k/s |

(Layout code's own output at 64 columns, printed from a throwaway test — not a screenshot.)

The rate now hangs off its cell's right edge, one gutter column short so it never butts against the next cell's dot. The slack lands between name and rate, where it separates two things read differently rather than misaligning either. idle right-aligns with the numbers for the same reason — it occupies the same slot.

Cell contents are split out into a small legend_cell helper so the placement is unit-testable rather than only observable on screen. Behaviour that did not change: a cell too narrow for both still drops the rate and keeps the name, truncating the name before dropping the entry; the row's +N overflow marker and the right-aligned Σ fleet total sit after the last cell as before.

Testing

cargo test --workspace green (exit 0, 0 failures). New tests assert the rate ends one gutter short of the cell edge for names of any length with a gap of at least one column, and that a cramped cell drops the rate before the name.

Spec 0167 updated.

Binaries

Only crates/cli changed → the relevant binary is construct:

/Users/moon/agentd/.claude/worktrees/legend-rate-right-align/target/debug/construct