refactor(rpiv-pi): name bash-timeout and lane-render constants; de-number agents comments

Give the remaining magic numbers names: the bash-timeout snippet cap
(SNIPPET_MAX_LEN, inclusive at 120, with boundary tests pinning the exact
truncate-at-121 behavior and the ASCII ellipsis), the lane console surface
floor and fallback rows, and the lane-list label-column overhead cells.
Cross-reference the deliberately duplicated git-exec timeout and the 30-min
bash/validation ceilings as separately owned.

Drop the brittle numbering in agents.ts (Step 1/2/3, Edge state 1/2/3) and a
stale CHANGELOG reference - the function names carry the sequence now.