Collapse Docker pull progress in non-TTY output

[sdairs]

Split out from #328.

Found during 0.4.0 RC local-command testing.

Problem

chctl local postgres start on a cold image emits a long stream of context-free lines (Pulling fs layer, Waiting, Downloading, Extracting, ... ×140) with no layer IDs or percentages. This is noisy for both coding agents and CI logs.

Expected behavior

When stdout is not attached to a TTY, collapse Docker pull progress to concise per-layer or per-phase summary lines, for example:

Pulling postgres:18... done (14 layers)

Interactive TTY output can retain richer progress.