Rule that the `body` extra field truncates at 500 chars like `issue view`,
resolving the spec's Principle 3 / Command Surface contradiction. Route the
`body` extractor through a new `truncatedBody()` FieldDef so `issue list`,
`issue create`, `pr list`, and `search` all present it exactly as the detail
views do, and add a `--full` flag to each to suppress truncation, keeping the
inline hint's "use --full" promise honest.
Implements `pr list` with the two policies later PR slices reuse:
client-side filtering with the filtered-set count line (ADR 0005) and
the official-first reviewDecision via parallel per-PR review fetches
(ADR 0006), extracted into src/review.ts.
API-supported flags map to their params (--state, --author→poster,
--label name→ID, --label-id, --sort, --limit, --fields); --assignee,
--base, --head, and --draft filter in-process after full pagination,
with the count line's total taken from the filtered set. --search is
refused with a redirect to `search prs`.
Adds a boolText field extractor and a shared parsePositiveInt helper,
the latter also adopted by issue list's --limit parsing.
